Putting A Gable Roof on my Garage

My garage is 25’4" by 42’2", and has a flat roof (rises maybe 18" over the 42’ length). I want to build a gabled roof over it. This will be a DIY project (I will have help, but will not be hiring a contractor). I live in north east PA. The garage is cinder block walls. I don’t want to use prefab trusses because I want storage space (or maybe an actual room). Off the top of my head, I am thinking of using 16’ 2x6’s for the rafters and plywood sheeting. I am planning on using metal roofing. Would rafters spaced 16" be normal for this?

This is in the very early planning stage as I am not planning on starting this project untill next spring.

Any help would be great.

You might have to move up to 2x8’s for that span, I’m not sure. If you are in an area governed by codes, the enforcement people can tell you.

My husband and I used attic trusses when we built our garage, and they were quite cost effective and easy to install. They were on 24" centers, and had metal braces so that once you swung them up into place (scary with only the two of us), the ends of the braces would rest against the previous truss, and you could just tap them in with a hammer. Made spacing very easy and accurate. You can see them in that picture, kind of.

Out of curiosity - your garage is 25 feet wide, but you propose to use 16 foot rafters? Sky hooks?

I believe the OP means a 16’ rafter on one side, meeting up with another 16’ rafter from the other side.

The attic truss option is good advice.

Not really.

You should get a structural engineer to look at your garage and size the framing lumber for you. You’re going to need a ridge beam and you should have the engineer check the foundation (if there even is one). Normally, you would need a building permit.

:dubious: Attic truss.

Looking at Renee’s picture, a room or storage would certainly be feasible.

Why are attic trusses bad advice? I didn’t make them up; they’re engineered to local codes and designed for exactly this application.

The walls are cinderblock, so I imagine this is a detached building with a slab foundation. Unless the walls are visibly failing, I personally think bringing in an engineer is overkill, when you can just go to a truss company and give them the measurements and the pitch you want, and they’ll make them and bring them to your door.

But it’s true, you might need a permit so you don’t get in trouble later. Depends on your location.

Attic or storage trusses are the way to go on this. And get an engineer to do a survey. If it has issues later on perhaps insurance wouldn’t cover a non permitted job.

I’m with the others. Talk to your municipality to get a permit and arrange for an engineer to do a site review.

You’re not just adding the dead load to the walls but you’re also adding shear from the added wind load acting on the trusses. Further, if you want to use it as storage, there’s more dead load that needs to be considered. In our area, storage areas need to be designed for 100 lbs per sq.ft.

The trussess I looked at online were much more closed in inside (I think that makes since). Like this http://www.google.com/imgres?imgurl=http%3A%2F%2Fvisual.merriam-webster.com%2Fimages%2Fhouse%2Fstructure-house%2Froof-truss.jpg&imgrefurl=http%3A%2F%2Fvisual.merriam-webster.com%2Fhouse%2Fstructure-house%2Froof-truss.php&h=384&w=550&tbnid=acFHObHvMOWu8M%3A&zoom=1&docid=Z5Cs9lUk-QZmRM&ei=RgSiU56iKcqVyATv3oHADA&tbm=isch&ved=0CDIQMygBMAE&iact=rc&uact=3&dur=225&page=1&start=0&ndsp=13

What you used seems to be what I am looking for.

And I was planning on getting a permit. I live on a main road and adding this roof would be very visible from the road. There wouldn’t be anyway to hide it. And of course I would listen to what they say and there advice. I just wanted to have an idea what was going on before hand.

Yes, it is detached from the house, and has a slab foundation.

The truss company should be able to design and supply trusses to meet your needs. A steep pitch will allow more headroom and storage room. My attached garage used trusses with additional vertical wall height and I have plenty of room.

It’s unlikely that your municipality will let you add a room above the garage w/o some significant foundation work.

Checking a span table (page 3), it looks like you will need to move up to 2X12s, (No1 or better) to span 25 feet and store any sort of a load up there.
Personally, I went with floor trusses and rafters for my 20 foot wide garage. I wanted to be able to store heavy stuff up there. If I ever do it again, I’ll probably use attic trusses.

Thanks for that; handy link.

Can you really span 25 feet without a center beam? I assume you need a center beam.
then there’s the problem if one end of that center beam rests on the center of a double-wide garage door. You’d need a cross-beam against the inside of the span over the garage door, to hold that end of the center beam, because guaranteed the existing configuration will not.
Now beams plus 2x8’s are eating into a lot of the head-space of the garage. Plus the center beam will probably go where your garage door opener would go.

This all assumes you want any room above your garage. Attic trusses can span that easily, but that assumes there is no real extra load in the space above the garage - no storage, no semi-finished rooms, etc. My 22-foot garage is spanned by trusses made of 2x4’s. I drywalled and insulated the garage, but that’s probably the limit of what the trusses were designed to take.

My storage attic trusses span 33’ with no issues. I don’t exactly recall, but they may be a mix of 2x4 and 2x6. They have about 2’ of wall built-in so I have over 6’ of head room near the center. The bottom chord looks to be 2x8.

But… Like a bridge, the triangular construction of the overall truss adds to its stability and strength - plus, the hollow center area must have specifications for how much load can be safely placed in the (I assume) hollow center space.

The trusses on my new house spanned almost 40 feet no problem, then the walls were built inside afterwards. This simplified construction - the entire ceiling was built and the vapour barrier put up in the open space before the interior walls went in, so there was no fiddling with plastic in small spaces. However, there was no load in the “attic” spaces, and no large open storage space.

Whereas my old house had 2x4 truss-like construction, but in the days before trusses, it was 2x4 across the ceiling 20 feet or more, 2x4 roof support, and vertical support (2x4) and a small horizontal brace (also 2x4) about 6 feet long across the top. This left a decent sized open room area, but without insulation it was not of any use. In some places it spanned over 20 feet unsupported.

I visited a place once that among other things, made trusses. They did this on a giant table that was a configurable jig - computers cut the 2x4’s and they were placed in the jig, then the metal pieces were pressed in on both sides to ensure a clean and complete construction. these guys used custom software to design a series of trusses to produce almost any roofline imaginable.

That would be the service you need if you want a properly engineered attic - they can design the trusses and ensure that the center storage room is properly supported or trussed, and what the allowable storage load would be.

Worst case, there are two 25-foot (metal?) “center beams” are every 14 feet or so and the posts that support these are against the solid walls instead of in the middle of the garage door; your entire ground floor interior is free of pillars. Then the upper floor joists need only span 14 feet.

I ordered my trusses from a place that did it exactly as you described. I said I wanted a lot of attic space so they designed it as such with a 7/12 pitch. Extremely pleased with the results.

regardless of whether you go the truss route consider running your top boards out the length of your overhang. This way you can use it to support the overhang as well as cantilevering boards between the last 2 trusses so they form support for the overhang. These connect the BACK of the fascia board and form an extremely sturdy overhang. the 2x4’s may flex a little but the fascia board adds lateral support so it’s like an L beam.

and it’s easy to make spacer boards that are notched 24" on center so you can space the trusses accurately and without a lot of effort. put 2 on each side while you’re nailing up the trusses and they’re spaced perfectly every time. Don’t forget the nails shown in picture or you WILL split the end of.

My storage area is over a 3 car garage. The vapor barrier is between the garage and the storage space. Most of what’s stored up there is decorations, screens, and storage boxes. High volume low weight stuff.

I’ll add that you need to put ties between the wall the trusses sit on. Well, maybe not so much with block, but I helped a friend build a three car garage many years ago. We set the trusses upside down on the walls and we’re going to flip them up and nail them to the top plate. We found that after about 6 trusses are hanging upside-down, the walls start to lean out a bit. We had to remove the trusses and tie the walls together and start over.