Roofing adding to metal roof, front porch, exterior elevations

Roofing adding to metal roof, front porch, exterior elevations


Expert: Mark Sundberg — 10/28/2007


We want to add a gable over the front porch and a shed roof over the back deck to our already metal roofed cape. We need instructions. How do we do that?

Thank you,

Kathryn and Bill


Aloha Kathryn and Bill,

Well, it’s quite as easy as just having a set of instructions, though, sort of, it is. That’s what a set of plans is, instructions to the builder(s) as to what and how to build whatever it is being built.

The first step for you would be to determine if you need a permit to undertake such a project, this would be from the local Building Department. It may be something like this doesn’t, but that’s becoming rarer and rarer. The Building Department should be able to tell you what they require for an application for such a permit. Generally that consists of the application form itself and a set of plans showing what the work is and how to do it. The plans will likely include a Site Plan showing the property and where any existing structures are and where the new work will be. Sometimes contours or spot elevations are required as well as setbacks and any legal controls on the property such as Rights of Way, Easements, etc. There will also need to be a Floor Plan and in this case, because you are doing roof work, a Roof Plan. Exterior Elevations and a Section through each part of the work would fill out the primary sheets. After that there may be sheet or two of details.

You can prepare the plans yourself, or hire drafter to do it. If you hire someone, they should know what to do. Something of this nature would likely not require either an Architect or an Engineer but best to check on that.

As to the work itself, if the front porch already has a roof, then you have to decide how much of the existing roof you want to retain and what the new gable will look like. Often it’s best to try and match the style of the existing structure. If there’s no existing roof, then you will need to erect posts at the outside edges of the porch, these will need to be at about 8′ to 12′ apart. For most purposes, 4×4 will be sufficient structurally but may look too spindly. The posts will have to have a footing to support them, unless there are already adequate footings for the porch. These would likely be 18" square and 12" deep with a galvanized metal base. You can usually buy pre-cast concrete piers with such molded in, so you just dig a hole in the ground, fill it up about 2/3 to 3/4 with concrete and set the pier into it, making sure it lines up with the rest of the structure.

On top of the posts will be a beam. With a gable roof, the beams will run from the house out both sides of the porch to the front. There are galvanized metal connectors that make attaching the beams easy and secure. You will want something that holds the roof down as well as holding it up. If you are in an area with high winds, you will want heavy duty hardware and you may well want to engage a professional to make sure the structure is adequate.

There will also be a beam at the middle where the ridge of the gable roof will be, called the Ridge Beam. On top of these beams will be the rafters, usually set at 16" to 24" apart. These will likely be 2x6s up to 2x10s or, if the porch is big enough, even 2x12s. Again, there is hardware available to tie the rafters to the beams. Plywood goes on top of the rafters and is usually nailed or screwed down. With a metal roof, it may be OK to use spaced sheeting, essentially 1x4s spaced 8" to 12" apart or even more. Some people will use 2x nailers. It depends on the metal roofing you are using. Then you nail or screw down the roofing. There may be some complications where the new porch roof intersects with the existing roof but without knowing the existing conditions its way too complicated with way too many alternatives and options to go through each.

Here are some good websites that explain the basics and provide some pictures.

None of these deal with metal roofing, which is a specialty unto itself. It can be tricky and unless you are familiar with it, I’d suggest hiring a roofer with experience in working with metal roofing.

Leave a Reply