poormansairforce
Well-Known Member
This post isn't about airplanes but it does show what can be done and the problems that can be solved with a little math and ingenuity. Just like we do with airplane structures especially spars.
I'm a General Contractor and have a customer who's house my son and I are renovating. It's in pretty bad condition and has needed many issues fixed. In this case the kitchen is a 20'x20' clear span room with the last 45" on each side ending in a clipped ceiling. The customer wanted to eliminate one of the clipped ceiling so we could add 2 big windows. This means we needed to extend the outside wall up and add a shed roof. Once I saw the trusses in the attic I knew we had a problem!
The trusses are hand made from 2x4s without diagonals, just 3 vertical members and zero gussets. To make matters worse they were 2' on center. The center of the ceiling was sagged 3" and each clip was sagged about 2 1/2". I calculated the dead and live loads at 16000 lbs! What to do? There was no way the roof could take the weight of the shed roof in that condition and shed roof has to hold the ends of the trusses after we cut them off which puts more weight on the peak area. There was no way to get any beam into the attic so it had to be built up just like many spars are constructed.
My dad and I have done many built up beams in attics. He passed away 1 1/2 years ago so now I'm teaching my son how to do these projects. So I laid it out to my son along with the math.
All work was done through a 24" x 27" scuttle hole in a 32" high attic at the peak. There is a fireplace that bumps out into the kitchen that has a shoulder we used as a bearing point. This makes the beam 18' 4" long. We added a column in the wall at the other end. Everything was glued and nailed. This is the material list:
4- 2x4 20' hand picked. $50
3- 2x4 8' verticals. $22
2- 4x8 3/4" BC plywood. $66
5 tubes PL Premium glue. $42
Airgun nails. $30
Total. $210
First we jacked the ceiling up so it was straight.
Then we applied a layer of 2x4s on the truss center verticals. This layer consisted of the top and bottom caps as well as compression members. The compression members served several functions. They allow attachment to the trusses to transmit the load, act as a stiffener for the web, as well as allow joining 2' wide web panels since we are working through a scuttle hole. We shimmed the caps as needed to ensure they were straight.
Then the shear web was glued and nailed to the first layer.
The last layer of top and bottom caps went on and then the rest of the plywood was used at each end to give it more strength as well as better bearing strength on the ends. Notice that there is a access hole in the center space of the beam. This provides access to the other half of the attic. I'm pointing this out since there is a thread on here about lightening holes in wood spars.
My son in the attic for referencing the small space available in which to work. He is 6'3" 220# so not a lot of room!
We let it cure over the weekend and removed the props today. It didn't move! I sized it to hold at least 8000 lbs since it will now hold part of the shed roof but it has a greater than 2 fos. Now we can proceed with the rest of the work. Hope you enjoyed seeing what's possible.
I'm a General Contractor and have a customer who's house my son and I are renovating. It's in pretty bad condition and has needed many issues fixed. In this case the kitchen is a 20'x20' clear span room with the last 45" on each side ending in a clipped ceiling. The customer wanted to eliminate one of the clipped ceiling so we could add 2 big windows. This means we needed to extend the outside wall up and add a shed roof. Once I saw the trusses in the attic I knew we had a problem!
The trusses are hand made from 2x4s without diagonals, just 3 vertical members and zero gussets. To make matters worse they were 2' on center. The center of the ceiling was sagged 3" and each clip was sagged about 2 1/2". I calculated the dead and live loads at 16000 lbs! What to do? There was no way the roof could take the weight of the shed roof in that condition and shed roof has to hold the ends of the trusses after we cut them off which puts more weight on the peak area. There was no way to get any beam into the attic so it had to be built up just like many spars are constructed.
My dad and I have done many built up beams in attics. He passed away 1 1/2 years ago so now I'm teaching my son how to do these projects. So I laid it out to my son along with the math.
All work was done through a 24" x 27" scuttle hole in a 32" high attic at the peak. There is a fireplace that bumps out into the kitchen that has a shoulder we used as a bearing point. This makes the beam 18' 4" long. We added a column in the wall at the other end. Everything was glued and nailed. This is the material list:
4- 2x4 20' hand picked. $50
3- 2x4 8' verticals. $22
2- 4x8 3/4" BC plywood. $66
5 tubes PL Premium glue. $42
Airgun nails. $30
Total. $210
First we jacked the ceiling up so it was straight.
Then we applied a layer of 2x4s on the truss center verticals. This layer consisted of the top and bottom caps as well as compression members. The compression members served several functions. They allow attachment to the trusses to transmit the load, act as a stiffener for the web, as well as allow joining 2' wide web panels since we are working through a scuttle hole. We shimmed the caps as needed to ensure they were straight.
Then the shear web was glued and nailed to the first layer.
The last layer of top and bottom caps went on and then the rest of the plywood was used at each end to give it more strength as well as better bearing strength on the ends. Notice that there is a access hole in the center space of the beam. This provides access to the other half of the attic. I'm pointing this out since there is a thread on here about lightening holes in wood spars.
My son in the attic for referencing the small space available in which to work. He is 6'3" 220# so not a lot of room!
We let it cure over the weekend and removed the props today. It didn't move! I sized it to hold at least 8000 lbs since it will now hold part of the shed roof but it has a greater than 2 fos. Now we can proceed with the rest of the work. Hope you enjoyed seeing what's possible.
Last edited:
