- Incorrect jack rafter length: Jack rafters that run from the ridge to the valley must be shortened incrementally as they approach the valley intersection. Each successive jack rafter is shorter by the same amount, called the common difference. Miscalculating this difference produces rafters that overshoot or undershoot the valley line.
- Wrong bevel angle: The side cut angle on a valley jack rafter changes with roof pitch. Using a generic 45-degree bevel on a steep roof produces a gap at the valley rafter interface that is difficult to fill without shims.
- Inadequate valley rafter support: Valley rafters that span more than 8 feet without intermediate support can sag under load, causing the roof sheathing to dip along the valley line. A purlin or strut under the valley rafter midpoint solves this.
Installing Roof Trusses for Complex Valley Roofs
Site-built rafters give the framer maximum flexibility for custom roof shapes, but engineered trusses reduce on-site labor and material waste for repetitive valley roof layouts. Installing roof trusses for complex hip and valley roofs requires coordination of truss placement with the valley intersections. Hip and valley trusses are typically designed as a series of girder trusses that support the intersecting roof planes, with jack trusses filling the space between girder trusses and the ridge line. The girder trusses at the valley intersection carry the combined load from multiple truss directions and must be installed with temporary bracing until the permanent lateral bracing is in place.
| Method | Best Use Case | Labor | Material Efficiency | Design Flexibility |
|---|---|---|---|---|
| Site-built rafters | Custom roof shapes, irregular plans | High | Moderate (some waste) | Maximum |
| Engineered trusses | Repetitive layouts, standard roof shapes | Moderate | High (low waste) | Limited to design |
| Hybrid (trusses + site framing) | Complex intersections, valley conditions | Moderate to high | High | Good |
For valley conditions where a standard truss layout does not align with the diagonal intersection line, a hybrid approach works best. Most of the roof is framed with standard trusses, and the valley intersection is site-framed using dimensional lumber rafters that tie into the adjacent truss chords. This approach captures the material efficiency of trusses for the bulk of the roof while preserving the geometric flexibility of site framing for the complicated valley intersection.
Double Beveled Rafter Techniques for Valleys
The valley jack rafters that meet the valley rafter require a double bevel cut: a plumb bevel on the face and a side bevel on the edge. The side bevel, also called the cheek cut, allows the jack rafter to lie flat against the side of the valley rafter. This is essential for proper load transfer through the connection. Double beveled rafter techniques for hip and valley roof framing provide a systematic method for marking and cutting these complex angles without trial and error.
The key to accurate double bevel cuts is the use of a framing square with the correct rafter table. On a standard square, the body represents the run (12 inches), and the tongue represents the rise. For valley jack rafters, set the square body to the valley jack rafter run and the tongue to the rise. The side bevel angle is read from the rafter table on the square tongue. After marking the plumb cut, rotate the square to transfer the side bevel angle across the edge of the rafter stock.
Valley Flashing: Protecting the Intersection from Water
Even perfectly framed valleys leak if the flashing is poorly installed. Valley flashing directs water down the intersection and onto the roof surface below, preventing moisture from penetrating the building envelope. The standard material is galvanized steel or copper, formed into a W-shaped profile that channels water on both sides of the valley centerline. Mastering W-shaped valley flashing installation requires bending the flashing to match the valley angle, extending it at least 6 inches up each roof plane, and installing it with concealed fasteners on the outer edges only. Nails through the center of the flashing create holes that leak.
Open valley versus closed valley flashing
Open valley flashing leaves the metal visible in the valley, with shingles cut back 2 to 6 inches from the valley centerline on each side. This exposes more flashing surface and provides a clear water channel. Closed valley flashing, also called woven valley, overlaps shingles across the valley so that no metal is visible. Closed valleys look cleaner but are more prone to ice damming in cold climates because the shingle overlap creates a raised profile that traps debris and snow melt. For roofs in snowfall regions, open valley flashing with a wider exposure (6 inches each side) provides better water shedding performance.
| Flashing Type | Visible Metal | Snow/Ice Performance | Installation Complexity | Climate Recommendation |
|---|---|---|---|---|
| Open valley | Yes | Excellent | Moderate | Snow zones, heavy rain |
| Closed (woven) valley | No | Poor | Higher | Mild climates, warm regions |
Drying in the Roof Assembly around Valleys
Drying in a roof means enclosing the structure with sheathing and underlayment so that interior work can proceed regardless of weather. For valley conditions, drying in requires careful coordination between the sheathing installation and the valley flashing. Drying in a roof with ZIP system and valley flashing uses a taped sheathing assembly that creates an integrated water and air barrier. The ZIP system panels are installed up to the valley edge, then taped to the continuous flashing strip that runs along the valley centerline. The tape seals the panel joints and bonds to the valley flashing, creating a continuous waterproof membrane that prevents wind-driven rain from entering through the valley intersection. This method reduces the risk of water damage to the roof deck before the final shingles or standing seam panels are installed.
Regardless of the sheathing system used, the sequence around valleys follows the same priority: install sheathing from the ridge down toward the valley, leaving a 1/2-inch gap at sheathing edges for thermal expansion, then install the valley flashing over the sheathing with the flange extending at least 4 inches onto each roof plane. Underlayment is then lapped over the flashing flanges so that any water that penetrates the roofing material is directed onto the underlayment surface and into the valley flashing channel.
Rafter Cutting Techniques for Valley Framing
Cutting rafters for valley intersections is more complex than cutting common rafters because each rafter has compound angles on both ends. A valley jack rafter, which runs from the ridge down to the valley line, requires a double bevel cut at the valley end to sit flush against the side of the valley rafter. The angle of this bevel changes with the roof pitch. Traditional farmhouse construction methods relied on rafter squares and on-site measurement to mark these compound cuts. Modern framers often use a construction calculator that computes valley jack lengths and bevel angles from roof pitch inputs, reducing layout time and cutting waste.
Common valley framing mistakes
- Incorrect jack rafter length: Jack rafters that run from the ridge to the valley must be shortened incrementally as they approach the valley intersection. Each successive jack rafter is shorter by the same amount, called the common difference. Miscalculating this difference produces rafters that overshoot or undershoot the valley line.
- Wrong bevel angle: The side cut angle on a valley jack rafter changes with roof pitch. Using a generic 45-degree bevel on a steep roof produces a gap at the valley rafter interface that is difficult to fill without shims.
- Inadequate valley rafter support: Valley rafters that span more than 8 feet without intermediate support can sag under load, causing the roof sheathing to dip along the valley line. A purlin or strut under the valley rafter midpoint solves this.
Installing Roof Trusses for Complex Valley Roofs
Site-built rafters give the framer maximum flexibility for custom roof shapes, but engineered trusses reduce on-site labor and material waste for repetitive valley roof layouts. Installing roof trusses for complex hip and valley roofs requires coordination of truss placement with the valley intersections. Hip and valley trusses are typically designed as a series of girder trusses that support the intersecting roof planes, with jack trusses filling the space between girder trusses and the ridge line. The girder trusses at the valley intersection carry the combined load from multiple truss directions and must be installed with temporary bracing until the permanent lateral bracing is in place.
| Method | Best Use Case | Labor | Material Efficiency | Design Flexibility |
|---|---|---|---|---|
| Site-built rafters | Custom roof shapes, irregular plans | High | Moderate (some waste) | Maximum |
| Engineered trusses | Repetitive layouts, standard roof shapes | Moderate | High (low waste) | Limited to design |
| Hybrid (trusses + site framing) | Complex intersections, valley conditions | Moderate to high | High | Good |
For valley conditions where a standard truss layout does not align with the diagonal intersection line, a hybrid approach works best. Most of the roof is framed with standard trusses, and the valley intersection is site-framed using dimensional lumber rafters that tie into the adjacent truss chords. This approach captures the material efficiency of trusses for the bulk of the roof while preserving the geometric flexibility of site framing for the complicated valley intersection.
Double Beveled Rafter Techniques for Valleys
The valley jack rafters that meet the valley rafter require a double bevel cut: a plumb bevel on the face and a side bevel on the edge. The side bevel, also called the cheek cut, allows the jack rafter to lie flat against the side of the valley rafter. This is essential for proper load transfer through the connection. Double beveled rafter techniques for hip and valley roof framing provide a systematic method for marking and cutting these complex angles without trial and error.
The key to accurate double bevel cuts is the use of a framing square with the correct rafter table. On a standard square, the body represents the run (12 inches), and the tongue represents the rise. For valley jack rafters, set the square body to the valley jack rafter run and the tongue to the rise. The side bevel angle is read from the rafter table on the square tongue. After marking the plumb cut, rotate the square to transfer the side bevel angle across the edge of the rafter stock.
Valley Flashing: Protecting the Intersection from Water
Even perfectly framed valleys leak if the flashing is poorly installed. Valley flashing directs water down the intersection and onto the roof surface below, preventing moisture from penetrating the building envelope. The standard material is galvanized steel or copper, formed into a W-shaped profile that channels water on both sides of the valley centerline. Mastering W-shaped valley flashing installation requires bending the flashing to match the valley angle, extending it at least 6 inches up each roof plane, and installing it with concealed fasteners on the outer edges only. Nails through the center of the flashing create holes that leak.
Open valley versus closed valley flashing
Open valley flashing leaves the metal visible in the valley, with shingles cut back 2 to 6 inches from the valley centerline on each side. This exposes more flashing surface and provides a clear water channel. Closed valley flashing, also called woven valley, overlaps shingles across the valley so that no metal is visible. Closed valleys look cleaner but are more prone to ice damming in cold climates because the shingle overlap creates a raised profile that traps debris and snow melt. For roofs in snowfall regions, open valley flashing with a wider exposure (6 inches each side) provides better water shedding performance.
| Flashing Type | Visible Metal | Snow/Ice Performance | Installation Complexity | Climate Recommendation |
|---|---|---|---|---|
| Open valley | Yes | Excellent | Moderate | Snow zones, heavy rain |
| Closed (woven) valley | No | Poor | Higher | Mild climates, warm regions |
Drying in the Roof Assembly around Valleys
Drying in a roof means enclosing the structure with sheathing and underlayment so that interior work can proceed regardless of weather. For valley conditions, drying in requires careful coordination between the sheathing installation and the valley flashing. Drying in a roof with ZIP system and valley flashing uses a taped sheathing assembly that creates an integrated water and air barrier. The ZIP system panels are installed up to the valley edge, then taped to the continuous flashing strip that runs along the valley centerline. The tape seals the panel joints and bonds to the valley flashing, creating a continuous waterproof membrane that prevents wind-driven rain from entering through the valley intersection. This method reduces the risk of water damage to the roof deck before the final shingles or standing seam panels are installed.
Regardless of the sheathing system used, the sequence around valleys follows the same priority: install sheathing from the ridge down toward the valley, leaving a 1/2-inch gap at sheathing edges for thermal expansion, then install the valley flashing over the sheathing with the flange extending at least 4 inches onto each roof plane. Underlayment is then lapped over the flashing flanges so that any water that penetrates the roofing material is directed onto the underlayment surface and into the valley flashing channel.
Rafter Cutting Techniques for Valley Framing
Cutting rafters for valley intersections is more complex than cutting common rafters because each rafter has compound angles on both ends. A valley jack rafter, which runs from the ridge down to the valley line, requires a double bevel cut at the valley end to sit flush against the side of the valley rafter. The angle of this bevel changes with the roof pitch. Traditional farmhouse construction methods relied on rafter squares and on-site measurement to mark these compound cuts. Modern framers often use a construction calculator that computes valley jack lengths and bevel angles from roof pitch inputs, reducing layout time and cutting waste.
Common valley framing mistakes
- Incorrect jack rafter length: Jack rafters that run from the ridge to the valley must be shortened incrementally as they approach the valley intersection. Each successive jack rafter is shorter by the same amount, called the common difference. Miscalculating this difference produces rafters that overshoot or undershoot the valley line.
- Wrong bevel angle: The side cut angle on a valley jack rafter changes with roof pitch. Using a generic 45-degree bevel on a steep roof produces a gap at the valley rafter interface that is difficult to fill without shims.
- Inadequate valley rafter support: Valley rafters that span more than 8 feet without intermediate support can sag under load, causing the roof sheathing to dip along the valley line. A purlin or strut under the valley rafter midpoint solves this.
Installing Roof Trusses for Complex Valley Roofs
Site-built rafters give the framer maximum flexibility for custom roof shapes, but engineered trusses reduce on-site labor and material waste for repetitive valley roof layouts. Installing roof trusses for complex hip and valley roofs requires coordination of truss placement with the valley intersections. Hip and valley trusses are typically designed as a series of girder trusses that support the intersecting roof planes, with jack trusses filling the space between girder trusses and the ridge line. The girder trusses at the valley intersection carry the combined load from multiple truss directions and must be installed with temporary bracing until the permanent lateral bracing is in place.
| Method | Best Use Case | Labor | Material Efficiency | Design Flexibility |
|---|---|---|---|---|
| Site-built rafters | Custom roof shapes, irregular plans | High | Moderate (some waste) | Maximum |
| Engineered trusses | Repetitive layouts, standard roof shapes | Moderate | High (low waste) | Limited to design |
| Hybrid (trusses + site framing) | Complex intersections, valley conditions | Moderate to high | High | Good |
For valley conditions where a standard truss layout does not align with the diagonal intersection line, a hybrid approach works best. Most of the roof is framed with standard trusses, and the valley intersection is site-framed using dimensional lumber rafters that tie into the adjacent truss chords. This approach captures the material efficiency of trusses for the bulk of the roof while preserving the geometric flexibility of site framing for the complicated valley intersection.
Double Beveled Rafter Techniques for Valleys
The valley jack rafters that meet the valley rafter require a double bevel cut: a plumb bevel on the face and a side bevel on the edge. The side bevel, also called the cheek cut, allows the jack rafter to lie flat against the side of the valley rafter. This is essential for proper load transfer through the connection. Double beveled rafter techniques for hip and valley roof framing provide a systematic method for marking and cutting these complex angles without trial and error.
The key to accurate double bevel cuts is the use of a framing square with the correct rafter table. On a standard square, the body represents the run (12 inches), and the tongue represents the rise. For valley jack rafters, set the square body to the valley jack rafter run and the tongue to the rise. The side bevel angle is read from the rafter table on the square tongue. After marking the plumb cut, rotate the square to transfer the side bevel angle across the edge of the rafter stock.
Valley Flashing: Protecting the Intersection from Water
Even perfectly framed valleys leak if the flashing is poorly installed. Valley flashing directs water down the intersection and onto the roof surface below, preventing moisture from penetrating the building envelope. The standard material is galvanized steel or copper, formed into a W-shaped profile that channels water on both sides of the valley centerline. Mastering W-shaped valley flashing installation requires bending the flashing to match the valley angle, extending it at least 6 inches up each roof plane, and installing it with concealed fasteners on the outer edges only. Nails through the center of the flashing create holes that leak.
Open valley versus closed valley flashing
Open valley flashing leaves the metal visible in the valley, with shingles cut back 2 to 6 inches from the valley centerline on each side. This exposes more flashing surface and provides a clear water channel. Closed valley flashing, also called woven valley, overlaps shingles across the valley so that no metal is visible. Closed valleys look cleaner but are more prone to ice damming in cold climates because the shingle overlap creates a raised profile that traps debris and snow melt. For roofs in snowfall regions, open valley flashing with a wider exposure (6 inches each side) provides better water shedding performance.
| Flashing Type | Visible Metal | Snow/Ice Performance | Installation Complexity | Climate Recommendation |
|---|---|---|---|---|
| Open valley | Yes | Excellent | Moderate | Snow zones, heavy rain |
| Closed (woven) valley | No | Poor | Higher | Mild climates, warm regions |
Drying in the Roof Assembly around Valleys
Drying in a roof means enclosing the structure with sheathing and underlayment so that interior work can proceed regardless of weather. For valley conditions, drying in requires careful coordination between the sheathing installation and the valley flashing. Drying in a roof with ZIP system and valley flashing uses a taped sheathing assembly that creates an integrated water and air barrier. The ZIP system panels are installed up to the valley edge, then taped to the continuous flashing strip that runs along the valley centerline. The tape seals the panel joints and bonds to the valley flashing, creating a continuous waterproof membrane that prevents wind-driven rain from entering through the valley intersection. This method reduces the risk of water damage to the roof deck before the final shingles or standing seam panels are installed.
Regardless of the sheathing system used, the sequence around valleys follows the same priority: install sheathing from the ridge down toward the valley, leaving a 1/2-inch gap at sheathing edges for thermal expansion, then install the valley flashing over the sheathing with the flange extending at least 4 inches onto each roof plane. Underlayment is then lapped over the flashing flanges so that any water that penetrates the roofing material is directed onto the underlayment surface and into the valley flashing channel.
- Determine the valley rafter run by measuring from the intersection of the ridge lines to the outside corner of the building in plan view.
- Calculate the valley rafter length using the unit run of the common rafter and the valley rafter unit length from the framing square rafter tables.
- Mark the plumb cut at the top end where the valley rafter meets the ridge board, using the valley rafter pitch angle on the framing square.
- Mark the seat cut and plumb cut at the bottom where the valley rafter bears on the wall plate.
- Lay out the jack rafter locations along the valley rafter, accounting for the 16-inch or 24-inch on-center spacing measured along the common rafter direction.
Rafter Cutting Techniques for Valley Framing
Cutting rafters for valley intersections is more complex than cutting common rafters because each rafter has compound angles on both ends. A valley jack rafter, which runs from the ridge down to the valley line, requires a double bevel cut at the valley end to sit flush against the side of the valley rafter. The angle of this bevel changes with the roof pitch. Traditional farmhouse construction methods relied on rafter squares and on-site measurement to mark these compound cuts. Modern framers often use a construction calculator that computes valley jack lengths and bevel angles from roof pitch inputs, reducing layout time and cutting waste.
Common valley framing mistakes
- Incorrect jack rafter length: Jack rafters that run from the ridge to the valley must be shortened incrementally as they approach the valley intersection. Each successive jack rafter is shorter by the same amount, called the common difference. Miscalculating this difference produces rafters that overshoot or undershoot the valley line.
- Wrong bevel angle: The side cut angle on a valley jack rafter changes with roof pitch. Using a generic 45-degree bevel on a steep roof produces a gap at the valley rafter interface that is difficult to fill without shims.
- Inadequate valley rafter support: Valley rafters that span more than 8 feet without intermediate support can sag under load, causing the roof sheathing to dip along the valley line. A purlin or strut under the valley rafter midpoint solves this.
Installing Roof Trusses for Complex Valley Roofs
Site-built rafters give the framer maximum flexibility for custom roof shapes, but engineered trusses reduce on-site labor and material waste for repetitive valley roof layouts. Installing roof trusses for complex hip and valley roofs requires coordination of truss placement with the valley intersections. Hip and valley trusses are typically designed as a series of girder trusses that support the intersecting roof planes, with jack trusses filling the space between girder trusses and the ridge line. The girder trusses at the valley intersection carry the combined load from multiple truss directions and must be installed with temporary bracing until the permanent lateral bracing is in place.
| Method | Best Use Case | Labor | Material Efficiency | Design Flexibility |
|---|---|---|---|---|
| Site-built rafters | Custom roof shapes, irregular plans | High | Moderate (some waste) | Maximum |
| Engineered trusses | Repetitive layouts, standard roof shapes | Moderate | High (low waste) | Limited to design |
| Hybrid (trusses + site framing) | Complex intersections, valley conditions | Moderate to high | High | Good |
For valley conditions where a standard truss layout does not align with the diagonal intersection line, a hybrid approach works best. Most of the roof is framed with standard trusses, and the valley intersection is site-framed using dimensional lumber rafters that tie into the adjacent truss chords. This approach captures the material efficiency of trusses for the bulk of the roof while preserving the geometric flexibility of site framing for the complicated valley intersection.
Double Beveled Rafter Techniques for Valleys
The valley jack rafters that meet the valley rafter require a double bevel cut: a plumb bevel on the face and a side bevel on the edge. The side bevel, also called the cheek cut, allows the jack rafter to lie flat against the side of the valley rafter. This is essential for proper load transfer through the connection. Double beveled rafter techniques for hip and valley roof framing provide a systematic method for marking and cutting these complex angles without trial and error.
The key to accurate double bevel cuts is the use of a framing square with the correct rafter table. On a standard square, the body represents the run (12 inches), and the tongue represents the rise. For valley jack rafters, set the square body to the valley jack rafter run and the tongue to the rise. The side bevel angle is read from the rafter table on the square tongue. After marking the plumb cut, rotate the square to transfer the side bevel angle across the edge of the rafter stock.
Valley Flashing: Protecting the Intersection from Water
Even perfectly framed valleys leak if the flashing is poorly installed. Valley flashing directs water down the intersection and onto the roof surface below, preventing moisture from penetrating the building envelope. The standard material is galvanized steel or copper, formed into a W-shaped profile that channels water on both sides of the valley centerline. Mastering W-shaped valley flashing installation requires bending the flashing to match the valley angle, extending it at least 6 inches up each roof plane, and installing it with concealed fasteners on the outer edges only. Nails through the center of the flashing create holes that leak.
Open valley versus closed valley flashing
Open valley flashing leaves the metal visible in the valley, with shingles cut back 2 to 6 inches from the valley centerline on each side. This exposes more flashing surface and provides a clear water channel. Closed valley flashing, also called woven valley, overlaps shingles across the valley so that no metal is visible. Closed valleys look cleaner but are more prone to ice damming in cold climates because the shingle overlap creates a raised profile that traps debris and snow melt. For roofs in snowfall regions, open valley flashing with a wider exposure (6 inches each side) provides better water shedding performance.
| Flashing Type | Visible Metal | Snow/Ice Performance | Installation Complexity | Climate Recommendation |
|---|---|---|---|---|
| Open valley | Yes | Excellent | Moderate | Snow zones, heavy rain |
| Closed (woven) valley | No | Poor | Higher | Mild climates, warm regions |
Drying in the Roof Assembly around Valleys
Drying in a roof means enclosing the structure with sheathing and underlayment so that interior work can proceed regardless of weather. For valley conditions, drying in requires careful coordination between the sheathing installation and the valley flashing. Drying in a roof with ZIP system and valley flashing uses a taped sheathing assembly that creates an integrated water and air barrier. The ZIP system panels are installed up to the valley edge, then taped to the continuous flashing strip that runs along the valley centerline. The tape seals the panel joints and bonds to the valley flashing, creating a continuous waterproof membrane that prevents wind-driven rain from entering through the valley intersection. This method reduces the risk of water damage to the roof deck before the final shingles or standing seam panels are installed.
Regardless of the sheathing system used, the sequence around valleys follows the same priority: install sheathing from the ridge down toward the valley, leaving a 1/2-inch gap at sheathing edges for thermal expansion, then install the valley flashing over the sheathing with the flange extending at least 4 inches onto each roof plane. Underlayment is then lapped over the flashing flanges so that any water that penetrates the roofing material is directed onto the underlayment surface and into the valley flashing channel.
Valley roof framing is one of the more technically demanding aspects of residential and commercial roof construction. A roof valley forms where two sloping roof planes intersect, creating an internal corner that channels water runoff toward gutters or drainage points. Proper valley framing prevents leaks, supports roof loads evenly, and maintains the structural integrity of the building envelope. Understanding the forces at work in valley roof framing and construction techniques for hip and valley roof systems is essential for any framer or contractor working with complex roof geometries. This article covers the framing principles, rafter cutting methods, truss installation, and flashing techniques that produce a watertight, long-lasting valley connection.
Understanding Valley Framing Fundamentals
A roof valley is not simply two roof planes meeting at a random angle. The valley line, or valley ridge, is the line of intersection between the two sloping planes. In a standard hip-and-valley roof where the intersecting roof planes have equal slopes, the valley ridge runs at a 45-degree angle to the exterior walls in plan view. When the intersecting roofs have different pitches, the valley ridge shifts off the 45-degree line, changing the geometry of the valley rafter and jack rafters. Valley framing for unequally pitched roofs requires additional layout steps because standard framing squares and speed squares are calibrated for equal-pitch conditions. Framers must calculate the true length of the valley rafter using the Pythagorean theorem applied in three dimensions, accounting for the different slope angles on each side of the valley.
Load paths in valley intersections
The valley rafter carries load from both intersecting roof planes down to the bearing walls or ridge beam below. Unlike common rafters that transfer load straight down, the valley rafter acts as a diagonal beam that collects load from the cripple jack rafters on each side. This concentrated load requires the valley rafter to be sized larger than adjacent common rafters. Building codes in most regions require valley rafters to be at least two nominal sizes larger than common rafters for the same span, or to be doubled when the valley length exceeds 12 feet.
Valley rafter layoutæ¥éª¤
- Determine the valley rafter run by measuring from the intersection of the ridge lines to the outside corner of the building in plan view.
- Calculate the valley rafter length using the unit run of the common rafter and the valley rafter unit length from the framing square rafter tables.
- Mark the plumb cut at the top end where the valley rafter meets the ridge board, using the valley rafter pitch angle on the framing square.
- Mark the seat cut and plumb cut at the bottom where the valley rafter bears on the wall plate.
- Lay out the jack rafter locations along the valley rafter, accounting for the 16-inch or 24-inch on-center spacing measured along the common rafter direction.
Rafter Cutting Techniques for Valley Framing
Cutting rafters for valley intersections is more complex than cutting common rafters because each rafter has compound angles on both ends. A valley jack rafter, which runs from the ridge down to the valley line, requires a double bevel cut at the valley end to sit flush against the side of the valley rafter. The angle of this bevel changes with the roof pitch. Traditional farmhouse construction methods relied on rafter squares and on-site measurement to mark these compound cuts. Modern framers often use a construction calculator that computes valley jack lengths and bevel angles from roof pitch inputs, reducing layout time and cutting waste.
Common valley framing mistakes
- Incorrect jack rafter length: Jack rafters that run from the ridge to the valley must be shortened incrementally as they approach the valley intersection. Each successive jack rafter is shorter by the same amount, called the common difference. Miscalculating this difference produces rafters that overshoot or undershoot the valley line.
- Wrong bevel angle: The side cut angle on a valley jack rafter changes with roof pitch. Using a generic 45-degree bevel on a steep roof produces a gap at the valley rafter interface that is difficult to fill without shims.
- Inadequate valley rafter support: Valley rafters that span more than 8 feet without intermediate support can sag under load, causing the roof sheathing to dip along the valley line. A purlin or strut under the valley rafter midpoint solves this.
Installing Roof Trusses for Complex Valley Roofs
Site-built rafters give the framer maximum flexibility for custom roof shapes, but engineered trusses reduce on-site labor and material waste for repetitive valley roof layouts. Installing roof trusses for complex hip and valley roofs requires coordination of truss placement with the valley intersections. Hip and valley trusses are typically designed as a series of girder trusses that support the intersecting roof planes, with jack trusses filling the space between girder trusses and the ridge line. The girder trusses at the valley intersection carry the combined load from multiple truss directions and must be installed with temporary bracing until the permanent lateral bracing is in place.
| Method | Best Use Case | Labor | Material Efficiency | Design Flexibility |
|---|---|---|---|---|
| Site-built rafters | Custom roof shapes, irregular plans | High | Moderate (some waste) | Maximum |
| Engineered trusses | Repetitive layouts, standard roof shapes | Moderate | High (low waste) | Limited to design |
| Hybrid (trusses + site framing) | Complex intersections, valley conditions | Moderate to high | High | Good |
For valley conditions where a standard truss layout does not align with the diagonal intersection line, a hybrid approach works best. Most of the roof is framed with standard trusses, and the valley intersection is site-framed using dimensional lumber rafters that tie into the adjacent truss chords. This approach captures the material efficiency of trusses for the bulk of the roof while preserving the geometric flexibility of site framing for the complicated valley intersection.
Double Beveled Rafter Techniques for Valleys
The valley jack rafters that meet the valley rafter require a double bevel cut: a plumb bevel on the face and a side bevel on the edge. The side bevel, also called the cheek cut, allows the jack rafter to lie flat against the side of the valley rafter. This is essential for proper load transfer through the connection. Double beveled rafter techniques for hip and valley roof framing provide a systematic method for marking and cutting these complex angles without trial and error.
The key to accurate double bevel cuts is the use of a framing square with the correct rafter table. On a standard square, the body represents the run (12 inches), and the tongue represents the rise. For valley jack rafters, set the square body to the valley jack rafter run and the tongue to the rise. The side bevel angle is read from the rafter table on the square tongue. After marking the plumb cut, rotate the square to transfer the side bevel angle across the edge of the rafter stock.
Valley Flashing: Protecting the Intersection from Water
Even perfectly framed valleys leak if the flashing is poorly installed. Valley flashing directs water down the intersection and onto the roof surface below, preventing moisture from penetrating the building envelope. The standard material is galvanized steel or copper, formed into a W-shaped profile that channels water on both sides of the valley centerline. Mastering W-shaped valley flashing installation requires bending the flashing to match the valley angle, extending it at least 6 inches up each roof plane, and installing it with concealed fasteners on the outer edges only. Nails through the center of the flashing create holes that leak.
Open valley versus closed valley flashing
Open valley flashing leaves the metal visible in the valley, with shingles cut back 2 to 6 inches from the valley centerline on each side. This exposes more flashing surface and provides a clear water channel. Closed valley flashing, also called woven valley, overlaps shingles across the valley so that no metal is visible. Closed valleys look cleaner but are more prone to ice damming in cold climates because the shingle overlap creates a raised profile that traps debris and snow melt. For roofs in snowfall regions, open valley flashing with a wider exposure (6 inches each side) provides better water shedding performance.
| Flashing Type | Visible Metal | Snow/Ice Performance | Installation Complexity | Climate Recommendation |
|---|---|---|---|---|
| Open valley | Yes | Excellent | Moderate | Snow zones, heavy rain |
| Closed (woven) valley | No | Poor | Higher | Mild climates, warm regions |
Drying in the Roof Assembly around Valleys
Drying in a roof means enclosing the structure with sheathing and underlayment so that interior work can proceed regardless of weather. For valley conditions, drying in requires careful coordination between the sheathing installation and the valley flashing. Drying in a roof with ZIP system and valley flashing uses a taped sheathing assembly that creates an integrated water and air barrier. The ZIP system panels are installed up to the valley edge, then taped to the continuous flashing strip that runs along the valley centerline. The tape seals the panel joints and bonds to the valley flashing, creating a continuous waterproof membrane that prevents wind-driven rain from entering through the valley intersection. This method reduces the risk of water damage to the roof deck before the final shingles or standing seam panels are installed.
Regardless of the sheathing system used, the sequence around valleys follows the same priority: install sheathing from the ridge down toward the valley, leaving a 1/2-inch gap at sheathing edges for thermal expansion, then install the valley flashing over the sheathing with the flange extending at least 4 inches onto each roof plane. Underlayment is then lapped over the flashing flanges so that any water that penetrates the roofing material is directed onto the underlayment surface and into the valley flashing channel.