how to extreme

Build a Deck Sunroof

Construction How-To, Decks, Decks, Roofing March 7, 2008 Sonia


Left: First step is layout. Locate the beginning edges of the sunroof on the house wall and use a plumb bob to mark the location.
Right: A homemade 3 x 4 x 5-foot square makes it easy to lay out post locations square with the building.

Plan the Right Design

The homeowners wanted a sunroof that would not only provide shade for relaxing and entertaining on the deck, but also provide more protection to the exposed south wall of the home and the large amount of glass in the window and two patio doors. The owners, however, enjoyed the solar warmth created in the winter, so the roof was designed to provide some sun reflection during the low-angle sun location of the winter months. The result is a sunroof that begins at 10 feet high on the house wall, is 8 feet high at the outside edge, and extends 10 feet from the building. The sunroof shown is 40 feet long. This also allowed for using standard materials, including 10-foot panels of Sequentia Super600 roofing. Before you begin construction of your sunroof, make sure to check local building codes on similar construction, materials and specific construction details. Also check for local zoning requirements and any permits needed.

A ledger board is attached to the house wall to anchor the rafters. Siding must be removed behind the board location and high enough to allow for flashing to be installed. Deck screws temporarily fasten the ledger board in place. Make sure the ledger board is installed level.

Getting Started

Construction of the sunroof framing is fairly straightforward, but it’s extremely important to get the framing square with the building. Otherwise the panels may not align properly, increasing or decreasing in the distance they extend from the rafter front edges. To determine the exact location and proper 90-degree angle for the corner posts in relation to the house wall, use a plumb bob on the wall to locate the first outside rafter.


Two methods can be used to ensure a square construction. The first is to locate the corner post locations with a tape measure, and then measure diagonally between a corner post and the opposite starting point on the house wall. Measure the other corner post diagonally to the opposite starting point on the house wall. Adjust the post locations until the measurements are the same. You can also use the “triangle” or “3-4-5” method. Measure 4 feet on the house wall. Attach a string line at the starting point and with someone holding the string line, measure and mark 3 feet out from the house wall on the string line. Move the string line in or out until the measurement between the two is 5 feet. Extend the string line to the outside location of the corner post. This creates a 90-degree angle.


Left: Drill starter holes and anchor the ledger board solidly in place with galvanized lag screws into the 2x house framing.
Right: In the case shown, the house was being resided with Western Red Cedar. After ledger board installation, the siding above the ledger board is installed.

Because I frequently lay out buildings, I’ve constructed a lightweight wooden triangle of those measurements. I can lay out the squared building quickly and easily with the triangle. Manufactured squares are also available for this chore.

Once the corner post locations are determined, run a string line between them and mark the inside post locations.


Roof Panel Detail

Support & Framing

The posts should be set on slabs and footings, and supported according to local building code regulations. In the project shown the posts were run through the deck to concrete supports below, and fastened to the under deck cross-member supports as well. The posts should be fastened to concrete slab/footings using approved steel anchor bolts. Use a 4-foot level and temporary bracing to hold posts in a plumb, upright position during construction. In the project shown, once the posts were plumbed they were anchored to the under-deck supports. You might wish to check into the Bigfoot Systems concrete tube forms for pouring supports.


Roof Blocking Detail

The house end of the rafters is supported on a ledger board. Remove the house siding from the ledger board location. In the case shown, the house was being resided and siding was installed up to the ledger board location. The ledger board was installed, leaving space for the roof covering and flashing, and siding installed above the ledger board. The bottom siding board is temporarily fastened in place in order to insert the metal flashing needed for the roof covering. The ledger board was leveled using a string-level for initial location, and then a 4-foot level to adjust as needed. Three-inch deck screws were used to initially fasten the board in place, and then lag screws were installed into the 2-by framing of the house wall. If fastening to masonry walls, use appropriate wall anchors. The fasteners should be installed on 16-inch centers as required.

Left: The sunroof shown is built over a deck. Post locations are marked on the deck using a scrap piece of 4 x 4 post.
Right: Starting holes are bored through the deck, and a saber saw or jigsaw is used to cut out openings for the posts to fit down through the deck.

All fasteners used with pressure-treated lumber must be corrosion-resistant. Phillips II High Performance DuraFast Coated screws recommended for pressure-treated lumber were used for all construction fastening. After years of pressure-treated lumber construction, these are my recommended fasteners. The box comes with a driver head that matches the screws and there is very little head stripping. A 2-by-2 support strip is fastened to the bottom edge of the ledger board to provide support for the rafters.

The project shown is attached to a bungalow type house that has 4-by-4 eave supports on the gable ends. To blend with the house, a “fake” eave support was constructed and screwed to the outside posts. The first or outside rafter rests on the outer end of this support. The remaining rafters are supported by headers fastened in place to both the inside and outside of the posts. These were located with their tops 8 feet from the deck. They must be level, and you will probably need two people for this chore. Two-by-four supports are added to the inside and outside of the posts to hold the headers. A 4-by-4 diagonal brace fastened to a 2-by-4 support piece anchors the headers to the posts and provides bracing and support.




As with laying out square, getting the first rafter laid out and cut properly is extremely important. I like to use a “scrap” but straight board to cut the first rafter. It should be cut and tested, cutting until you get the correct angles and cuts. Once the trial rafter is cut, and temporarily installed, again make sure the rafter and house wall are perpendicular or at a 90-degree angle. Mark the location, remove the trial rafter and use it as a pattern to cut the first rafter. After cutting, recoat any cut ends with protective finish. Install the vertical panel support strips on the rafter tops using galvanized nails. A finish or brad nailer and galvanized nails makes this chore easy.



Temporarily install the first and second rafters. The rafters are located on 24-inch centers. The outside rafter is anchored in place with a screw from the underside of the 2-by-2 support block into the underside of the rafter end. A 22-1/2-inch filler block is placed inside and next to the outside rafter. Fasten the inside rafter against the filler block with a screw from the underside of the support strip. Use a scrap piece of roofing panel on the outer end to test for fit and precise rafter location. Check on the house end as well. Then slide the flashing up under the siding and test it on the roof panel and rafters. Once adjusted so it all fits properly, permanently anchor the rafters in place with screws through the rafters and into the filler block. An outside filler block is also required and a horizontal cross strip must be fastened to the top of it. The outer ends of the horizontal cross strips must match the crown profiles of the vertical edge strips. Again, fasten with brads or galvanized finish nails.

Left: The sunroof in this article is designed to complement a bungalow-style house with eave supports. False eave supports are made in the shop.
Right: The false eave supports are fastened to the outside posts.

I fastened the filler blocks in place by first pre-drilling pocket-hole screw holes on the back side using a Kreg Pocket Hole tool. Anchor the block between the two rafters and then screw the rafters into the filler block. From this point on, it’s a matter of positioning a rafter, then screwing it to the outer ends of both filler blocks. Interior filler blocks, again topped with horizontal cross strips, are placed between the rafters, spaced as shown in the drawing titled Roof Blocking Detail located five paragraphs above.

Left: The first rafter is installed against the house wall and rests on the false eave support. The rafter is squared with the house wall and anchored to the eave support.
Right: A house-wall filler block is installed and then the flashing installed.

You can install the rafters, then cut and fit the individual interior filler strips in place, but on a job of this size, I found it more convenient to “pre-assemble” the components. First, all filler blocks were cut to precise lengths using a Ridgid Exactline Compound Miter saw supported on their new Miter Saw Utility Vehicle support. The Repeat-A-Cut fence and a stop block made it quick and easy to cut all strips to precise lengths, as well as the horizontal panel support strips. All strips were then fastened in place. The interior support strips were fastened to the rafters before erecting the rafters. This was easier for the location than working from a ladder. The rafters were fastened in place, and the loose ends of the interior support strips were anchored to the mating rafter. You may need two people to lift and fasten these assemblies in place.


Left: The headers are fastened to the posts, making sure they are plumb, and a support block is screwed to the post below them.
Right: An inside support block with a 45 degree diagonal 4 x 4 fastened to it is anchored to the post.

An additional 2-by-4 filler block with horizontal cross strips is installed against the ledger board and serves as an anchor for the end of the corrugated roof panels and the metal flashing.