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Re: Short Cantilevered Extension to Cement PorchFrom: info@builderswebsource.com
Category: Decks
Remote Name: 63.198.181.43
Date: 27 May 2002
Time: 12:36 PM
CommentsYou have a 3-foot-wide concrete porch across the front of your house, roughly 2 feet above grade. To provide additional clearance for deck chairs, you would like to expand the width by an additional 1.5 feet with a cantelevered wood extension. You would like to do this without adding intermediate posts as the frost line is 42" below grade. Assuming the foundation supporting the front portion of the concrete porch is filled solid (and hopefully reinforced with rebar), you can probably support the proposed cantelevered section with custom plate steel traiangular supports with flanges. The angle should be 45-degrees, which will help to transfer the load back to the foundation. The flanges should be bolted in several places to the foundation wall (you may need a concrete drill/roto hammer for this), and positioned in height such that the top of the wood decking is flush with the existing concrete deck. If the existing porch slopes, you'll need to take this into account when designing the angle supports. Alternatively, you may be able to build a similar structure out of pressure treated lumber. We would bolt on a 3x6 pressure-treated ledger (at least 6" above grade) on to the existing foundation, using 5/8" lag bolts every 12", staggered slightly. You'll need to use special concrete anchors specifically designed for this type of situation. Build out your supports at a 45-degree upward angle from the foundation and tie those into a front support beam. Similarly, add another ridge board just below the bottom of the existing concrete and build out straight supports. Using 3x6 should give you a plenty stout support structure. Then add your decking and front fascia as you normally would. Any deck must be designed for a 40 psf live load and 10-20 psf dead load, plus any expected snow loads. To make sure your deck doesn't sag, you'll need to build supports as often as necessary to support the required load and take out any springy feeling. Probably a 24" maximum span between supports is tops. These recommendations are illustrations only. You must ensure that any design you pursue is built to the highest safety standards that take into account the specific conditions of your home. If in doubt, contact a licensed structural engineer who can run calculations for you and recommend the quantity and size of steel or wood members. Builders Websource
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