How to Build Roof Over Deck

A deck can transform your house, add extra living space outside, and boost the overall value of your home. The downside is that a deck isn’t a permanent living space – it is weather-dependent. Recently I’ve seen some neighbors try to solve this problem with a roof. I’ve considered it myself, but I wasn’t sure exactly how to build a roof over a deck.

To build a roof over a deck, you need to connect the new roof framing to the existing home. The easiest way is to use posts and beam construction with rafters connecting the beam to the home. Other ways involve removing a portion of the existing roof, adding trusses, and other framing options.

In this article we’ll cover all your options when it comes to adding a roof to your deck. While a deck roof entirely depends on how your current deck sits with your house, we’ll also give a general overview of DIY deck room construction.

How to Build Roof Over Deck

What is a Deck Roof

A deck roof is a roof that connects to your existing roof and covers part or all of your exterior deck. It can cover a screened-in area to create a porch or just act as a covering to your deck for shade and all-weather use.

A roof covering the deck is framed similarly to a house roof and connects mechanically to your house wall or roof. The roof is supported by beams and posts on the exterior, which are anchored to the ground – not the deck structure – with concrete to provide a stable foundation.

Should I Put a Roof Over My Deck?

A roof over a deck is a great option for people who want to use their deck – rain or shine. Or, for those who live in very sunny and hot areas, it makes outdoor living more bearable by providing permanent shade.

While a roof over a deck may not be ideal for all geographies or homes, having a covered space on the exterior of your house is practical for a variety of reasons:

Pros

  • Weather protection – rain, snow, and sun
  • Provides year-round outdoor use
  • Can act as a greenhouse with certain types of roofing or siding
  • Keeps outdoor items dry, such as clothes, furniture, and barbecue

Cons

  • Reduces sunlight
  • Cost
  • Potentially requires digging new footings for roof

Can Your Deck Support a Roof?

A deck alone can never support a roof. For instance, you cannot rely on your deck joists or beams to support your roof as well as your deck. Load tables for joists and beams consider 10 psf dead loads, which is the amount of lumber used on the deck alone – not a deck and a roof. Therefore, adding a roof’s weight onto a deck negates the structural integrity of the deck.

A deck roof will need to be supported by posts and a beam. The posts will need to be on concrete footings, deep enough to go beyond the frost line in your area. A beam will connect the posts and will be sized according to the local building code. The rafters will support the roof itself and connect the beam to the house.

If you already have appropriately sized posts supporting your deck, there is the possibility of integrating existing deck posts with the roof posts; however, in most cases, the deck roof will require new footings.

Deck Roof Types

There are several different styles of roof that you can put over your deck. The style used is usually dictated by the location of your deck in relation to the existing roof of the house. Here are the most common options for a deck roof:

Gable

A gable roof is ideal for situations where slang roofs are not possible due to low rooflines. This type of roof is more complex to build because it requires two beams perpendicular to the existing roofline. You must then connect the beams to the house roof framing. The deck roof can either be framed with trusses or rafters that attach to each beam.

Slanted

A slanted roof is one of the most common deck roofing choices. The slanted roof slopes downward from the existing roof. It is supported by posts and one beam. Rafters attach the beam to the house roof framing. A slanted roof is more straightforward than a gable roof because it involves one beam instead of two.

Hip

A hip roof is a mix of a gable and slant roof. It uses either rafters, trusses, or both in combination to cover a deck. One end is supported by two posts and a beam. Two more beams connect either side to house roof framing. Rafters connect the beams to a ridge beam, which also connects to the existing house framing.

Deck Roof Materials

There are several options homeowners choose when covering their deck roof. While it makes sense to have the same deck roof material as your existing roof, you can go a different route to add aesthetic value or a practical space beneath your roof, such as a greenhouse.

Polycarbonate Roof Panels

These roofing panels resemble plastic in that they are semi-transparent, allowing light to filter through while keeping the weather out. While not as durable as shingles or metal roofing, they are strong enough to withstand most outdoor conditions. Installation is straightforward, as the panels can attach to 1x wood strapping with special screws and washers.

Shingles

If you want to keep your deck roof to meld seamlessly into your existing roof, then shingles are a great option. Integrating shingles into your existing roof involves flashing valleys created by the gable or hip roofs or simply sliding new shingles beneath the existing shingles if installing a slanted deck roof.

Metal Roofing

Adding metal roofing to your deck roof can make it an attractive feature for your home. If you have a different type of roofing on your existing home, integrating metal can be difficult. However, metal roofing itself is the most durable option and will also provide the greatest return on investment for your deck roof.

How to Build a Roof Over an Existing Deck: Step By Step

In this guide, we’ll go over how to build a deck roof over your deck. This step-by-step overview will cover the installation of a slanted deck roof. Gable and hip roofs will vary, particularly in how you connect their framing to your existing roof, but the construction of posts and beams will be similar to the slanted roof.

Make a Plan

You’ll need CAD drawings or a plan done by a professional engineer or planner before you embark on your project. You will need a building permit from your local building department, and they will require a plan before a permit is issued. Once you have your plan, you can go ahead and order materials.

Prep House for New Roof Framing

If you install a slanted roof over your deck, your deck roof rafters will have to attach to your existing roof rafters or trusses. To do this, you’ll have to remove a section of existing roofing materials and sheathing, plus soffit, fascia, and any gutters that are in the way.

If your new deck roof connects to a flat, vertical face such as a home’s exterior wall, you’ll need a ledger board fastened to a rim joist. You’ll need to remove the siding to fasten the ledger. Once in place, the ledger can support beams or joists that will support rafters or trusses for gable or hip roof construction.

When installing the ledger board, you’ll need to put flashing over the top edge of the board. This flashing should go up and under your siding. You should use an adhesive to affix it to the sheathing beneath the siding.

You’ll need to bend the flashing to sit flush over the top ledger board edge. The flashing should cover the top half of the ledger board. Once the flashing is installed, the rafters will sit on top of the flashing.

Install Post Base Connectors

When installing a deck roof, you cannot simply fasten the posts to support the roof to the deck surface. Deck boards – even deck framing – cannot support more than it was designed for – a deck.

You have two options. Dig new concrete footings for posts that will support the roof structure above the deck. That requires digging below the frost line, installing 10” sonotubes, and filling them with concrete. Backfill and install a 6×6 post bracket on top of the form.

Or, you could integrate your roof support posts to sit directly above your deck posts. They will have to sit on top of your beam, and you can use strapping to connect the deck posts to the roof posts sitting on top.

Install Posts

Use 6×6 posts to support your deck roof. Your posts will sit atop 6x6 post brackets. Install them using the fasteners specified by the type of bracket you are using.

When installing posts on top of existing deck beams, you will use the strapping as specified above to secure the roof post to the deck framing.

Install beam

You’ll need to consult a beam table to determine the type of beam you’ll be installing between your deck roof posts. Once you figure out the size, the beam can sit on top of the 6×6 posts or you can notch one side of the posts to have the top of the beam sit flush with the top of the post.

Beams must connect to posts using approved fasteners. Simpson provides some post beam connectors that are designed to use either 16d nails or Simpson structural screws.

Install Rafters

Once you have a beam, you can begin attaching your rafters. Since you’ve already prepped the area of your existing roof for rafters, this is simply a matter of fastening a rafter to the beam and the existing roof framing.

Depending on the height of your deck and the slope of your roof, your rafters could sit on the top plate of the exterior wall of your house. There you would fasten them to the top plate with a rafter bracket and use 16d nails to fasten them to the adjacent roof truss or rafter.

IF the slope of the new deck roof goes above the top plate of your existing wall, you’ll nail your new deck roof rafters to the existing rafters on your house with 16d nails. The beam to rafter connection requires brackets and nails as approved by the bracket manufacturer.

Install Roof Sheathing

If installing shingles, you’ll have to sheath your roof with OSB or plywood. 7/16” OSB is an example of roof sheathing, which comes in 4×8 sheets. If using metal roofing, you can either put sheathing or 1×3 strapping perpendicular to your rafters.

The metal roofing can then be screwed into the strapping. This is cheaper than sheathing a roof and potentially more aesthetically pleasing. Polycarbonate roofing is similar to metal roofing in that you can either place it on solid sheathing or strapping.

Install Roof Covering

The last step is installing your roofing material. This step is no different than installing roofing material on the house or shed. Follow the manufacturer’s instructions and take care if integrating shingles or metal to an existing roof.

How to Build a Gable Roof Over an Existing Deck

Building a gable roof over a deck is similar to building a slanted roof, with a few differences. First, you will need two more beams that attach from the house framing to the new beam you’ve installed that is supported by the new posts that will support the ends of the gable roof.

The new beams will be two or three 2x pieces of lumber laminated and supported by joist hangers on the new beam and the ledger board on the house side. These new beams will support trusses, which will be held in place by brackets.

Tying the new gable roof into the existing house may require you to remove some of the old roofing from the existing house. In some cases, the gable roof will be flush with a wall and not a roof, and this will make your life easier. Using flashing to join the house wall and new roof will help waterproof that joint, provided the flashing goes up and under the house siding.

How Much Does It Cost to Build a Roof Over a Deck?

Expect to spend around $5,000 to build a roof over a 12×12 deck. Depending on the materials you use and the size of your deck, spending $10,000 is not uncommon. A total price range of $2000 to $10,000 would cover most roofs put over decks.

Do I Need a Permit to Add a Roof To an Existing Deck?

You need a permit to put a roof over your deck. For one, it is a safety concern. Failure to properly fasten the roof to the house could lead to collapse and injury. Secondly, if you don’t attach the roof to the house properly, you could invite significant water damage into your house, resulting in major damage.

Any project involving framing or adjusting existing house framing will require a permit, regardless of where it is on your property. However, unlike a shed, even the smallest addition to your existing house roof will require a permit.

Conclusion

When it comes time to frame a roof over your deck, the most important part is creating an easy to follow framing plan. First, your local building department will require drawings, so you’ll need one anyway. Second, roof framing can get complicated. A diagram will save you some serious head scratching while you are in the middle of your build.

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