How to Modify Wood and Attic Trusses
Here I am alongside a truss being used over a giant garage. This truss has a special elevated bottom chord. Photo credit: Todd Fratzel
Modify Wood and Attic Trusses TIPS
- Trusses can be modified or changed
- Structural engineer must be consulted
- WATCH truss videos below!
- Replace with common rafters
- CLICK HERE to Get Tim's FREE & FUNNY Newsletter!
Mike, from Cleveland, Ohio, wrote to me:
Tim, great reading your tips. I've got a question, I would like to convert the attic above my garage into a living space. Access is not an issue as it's also in front of another room upstairs that I can put a door in the wall.
There's plenty of room to make a 12 x 12 room with 10-foot ceiling at its peak.
Common Trusses
Unfortunately, my home builder had framed out the attic using a common truss system utilizing 2x4's (see attached picture of exact type, although my roof is much steeper, and no middle non bearing wall below).
This is a graphic Mike supplied to me. I don't know if he drew it, but I sort of doubt it. Image credit: Unknown skilled person
There's enough space to switch the floor joists that are 2x4s with 2x10s or 8s, and/or sistering them. The main issue I have what to do about the truss itself (2x4 webs, 2x4 chords, etc.). From what I imagine larger rafters would need to be in place of those 2x4 top chords.
Is this possible, and how costly would a project like this be? (just the structural engineering and framing aspect to allow for live loads and support the roof). I'm trying to decide if it's all worth it."
Changing Trusses
You can modify the trusses, but it's an enormous amount of work. Also, if you decide to do this, you MUST work hand-in-hand with a licensed structural engineer that's familiar with wood trusses.
Huge Challenges
Here's one challenge. If you feel you'll be sliding new larger common rafters up inside the attic alongside the existing trusses, you're dreaming.
You'll have shingle nails in your way that extend through the roof sheathing. You'll also be dealing with a low heel height on the existing trusses.
Heel Height
Most common trusses have a miserable heel height of just over four inches.
The heel height is the vertical distance up the truss face where it passes over the OUTER EDGE of the building line or supporting wall. This is typically where the face of the exterior wall sheathing is.
Wood Truss Videos
Watch these two videos to see very unique things truss engineers can do to create higher ceilings and large overhangs.
Attic Trusses
The sad fact is your builder could have installed attic trusses over this garage for just slightly more than what the existing trusses cost. Attic trusses have a rectangular shape inside each truss.
If the roof slope is steeper than 9 inches in 12 inches of run, it doesn't take much width to end up with a nice room 12 feet wide with an 8-foot ceiling. I have this above my own garage.
Look at this photo of the space created by attic trusses at my home. You can't see the floor, but the window sill is just about 32 inches up off the floor. The flat ceiling that connects the two sloped parts of the truss is just out of the photo frame.
This is the end wall of the attic above my garage. The space is 12-feet wide and ceiling height is 8 feet. I didn't build this house, but the architect did everyone a favor by making the vast space above the 40-foot-long garage out of attic trusses. I took part of this giant room and made a cozy man cave ham-radio shack. © 2017 Tim Carter
Demo Roof
You may find it easier, as crazy as this sounds, to rip off the existing roof and start over. I guarantee you it would be FASTER.
You'd be able to use regular 2x10 or 2x12 rafters and create a gigantic room where now exists useless space.
If you have limited manpower, you'd do this in sections. I'd just rip off about six feet of existing roof at a time, set the new rafters, sheath them and cover them with tar paper.
You'd have a small gap between the new and old roof you'd need to weatherproof in case rain was in the forecast.
It would help TREMENDOUSLY if you increased the new roof pitch so the new roof ridge board would rest on top of your existing trussed roof.
Thanks for the article! I thought it was interesting that attic trusses shouldn't be installed over the garage. Having the trusses over the garage and then wanting to add a room over the garage can cause problems, especially since the trusses are so important to the structure. I had my upstairs living room redone recently and we ended up moving a wall a few feet but couldn't go further than the truss at the edge of the house. Though we couldn't make out a square wall, just moving the flat portion of the wall over a couple feet made a huge difference to the house. I really appreciate your advice, I hope to apply these tips in the future.
Thanks for sharing this! Seeing the amount of work that goes into making the modification happen definitely makes taking the roof off seem more appealing if it can be done. Either way, it looks like it's going to take quite a bit of manpower.
Informative - I have a contractor in place to redo the roof already (it's 20+ years old and insurance will cover it). So I assume they may know a contractor that can redo the attic space over the garage so I can use it as storage? I have less than half my garage for my woodworking and looked up in the attic earlier thinking to myself man if only I could cut those angled monstrosities and somehow make them vertical I could put some 1/2" - 3/4" Plywood down and store the boxes of stuff I currently have in the garage up there. I will contact them on Monday and see if we can have that done when they redo the roof (might as well do it all in one shot right?)
You state "Most common trusses have a miserable heel height of just over four inches." Are you implying the common heel height is too short so it conceals part of the exterior wall, which is not desirable?
The low heel height makes it so you can only have 3 to 6 inches of insulation in the ceiling at the corner where the ceilings meet the exterior walls. You should always maintain a 2-inch free air space above the insulation for ventilation. Do the math.....
Using 'Energy Trusses' fix that. They are common in the arctic and not much more expensive than standard trusses. They allow for much more insulation and clearance between truss and wall.
newsletter to receive expert advice
can i move my garage web in the attic from the tilt position to vertical position so i can make a hole to transient through to the rest of the attic ?
Hello,
My garage has Howe Girder trusses that are 24" on center spanning 22' using 2x4's. The first truss is 16" from the exterior wall then the next truss is 8" then 24" on center from then on. From the center of the truss to the vertical bracing it is 62". I want to cut out the bottom cord along with the angle bracing for the first two trusses mentioned above. From a structural standpoint is this possible? If so what modifications need done in order to do so?
Hi my name is Tom I'm from right out side of Philadelphia and my question is, I have a 40'×70' 12in cement garage that was in a fire in 2000 and my grandmother had the flat roof replaced with a huge trust roof I'm not quite sure of the pitch but the bottom cord to the top cord in the center must be 15 to 18 foot and they span the hole 40' with no support and the top and bottom cords are 2×6 with 2×4 webbing 2' on centers its 35 of them . I really wish I was older and wiser when this took place so she would have had attic trusses installed but here we are . Lol . I found 20 -40' attic trusses for sale on Facebook market delivered for 7800.00 and I am wondering if it is possible to dismantle each one piece by pice and reconstruct them piece by piece back together up in the ceiling or am I living in a fairy tale thinking that that's possible I would really appreciate your Insight on this matter thank you
I'm looking to figure out how to create a stairway leading into my attic space. We have the same thing as your garage where we used attic trusses to have a space above the garage and stairs to lead up there. The garage was a package that came with all the lumber and plans from a hardware store near by. The plans never showed how to frame or modify the trusses to account for the stairs though. I can't find any videos either explaining it and wanted to know what you did.