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How To Build A Roof Over A Deck

Installing a porch roof over an existing deck is usually not recommended unless the deck was originally designed to support a future porch.  Typical decks are designed to support 55 psf (lbs per square foot).  Porch decks require 25 additional psf for roof loads for a total of 80 psf.  As a result most decks have inadequate footings to support a new porch roof.  The footings for porch decks must be larger than deck footings.  Many porches use 22"+ diameter corner and intermediate footings.  Gable end porches will also require an additional footing in the center of the side rim to transfer the truss or rafter loads to the footings because the framing of the roof is perpendicular to the floor framing.  Porch footings must be positioned on the perimeter of the porch to directly transfer the loads to the footings.  Decks with cantilevered beams are not designed to support porch roofs.

The original foundations could be removed and enlarged to accommodate the new weight of the roof. If the posts supporting the roofs are placed directly on the deck structure below, there are a few considerations to make. The posts should stack directly above a support post below, and not within the span of a beam. Be sure that the deck floor frame is at least as thick as the entire cross-section of the post above and below. A 1.5-inch thick rim joist cannot support a 3.5-inch thick post above. Blocking must be installed adjacent the rim joist.

To avoid any modifications to the existing deck below, or to facilitate future replacement of the deck below the roof, the roof can also be designed independently from the deck. New foundations piers would then be installed and sized only with the roof in mind.


Comments, Questions and Reviews


Good info...even a small town country girl can comprehend. Thanks

posted by adkooch at 7/28/2015 4:11:39 PM

Will you cite your references for the information in this article?

posted by mbailie at 4/16/2015 1:39:07 AM

Why does it seem that all builders want to tie a roof into the deck. I can not find a builder who will even consider what I ask. All I want is a cover over my deck ie as if the deck wasn''t there only a patch of earth.

posted by Edward Kirk at 2/6/2015 11:06:47 AM

we are planning on building a "cover" for our deck. Just a simple structure with 2x4''s and 4x4 posts with a corrigated roofing . What is the recommended spacing for the joists? thanks so much

posted by lhotzwik at 7/13/2014 8:38:27 AM

It depends on the size and design of the deck.

posted by mike at 7/14/2014 10:56:21 AM

I found you instructionsvery helpful. A lot of insight. However I would like to see a few more pictures.

posted by Alton at 6/10/2013 6:07:08 PM