Framing with rafters and joists

[75gmck25]

My 1940 brick garage is about 11x20 feet with a roof pitch of about 7/12. When they built the roof they used standard rafters and cords, but only put 2-3 ceiling joists at each end across the garage, spaced about 16" on center. The middle of the garage area just has the rafters, cords, and open space. The "loft" storage area created by the joists on each end is floored with plywood but you have headroom in the middle all the way up to the top cord.

I plan to increase the height of the side walls so I have more headroom to work, and I may need to reconstruct the roof completely if the wood is damaged during the deconstruction and reconstruction.
Question: If I reframe the roof can I use the same type of structure, where there are joists spanning the garage for a few feet on each end, but no joists in the middle section? The walls are brick facing on block, so they are very solid and not likely to spread outward if the two walls are not tied together by joists in the middle section.

Thanks,

Bruce

 

[the GOAT]

You will need to have a rafter ties on the lower third of each rafter if you rebuild the roof more or less the same.... But there are alternatives to the code such as a structural roof beam which would require no ties/joists. and of course scissor trusses are always an option.

 

[-Brent-]

I think the Goat meant the upper third on the collar ties.

 

[Falcon67]

You should be able to lift the entire roof structure as a unit, brace in place and then raise your wall height. 11x20 isn't really a big deal. You might have to place some temp joists while the roof is up.

 

[theoldwizard1]

When they built the roof they used standard rafters and cords, ...

I have never heard the term "chord" used outside of the context of a roof truss.

Are you refering to purlins ?

Question: If I reframe the roof can I use the same type of structure, where there are joists spanning the garage for a few feet on each end, but no joists in the middle section? The walls are brick facing on block, so they are very solid and not likely to spread outward if the two walls are not tied together by joists in the middle section.

In theory, yes, but you need to take a lot of picture and measurements.

I said in theory, because even though it has been perfectly sound all these years it is not a common building practice and the local building authority may not approve it as a replacement, especially it the additional height you want to add does NOT use that same construction technique (block and brick).

The reason this has worked is because of your thick walls !

If you are planning to raise the roof as one piece I would temporarily install rafter ties on the rafters that have none.

 

[Radix2]

What they did is create trusses at each end of the garage to hold a ridge beam in the center - that is why you do not need ceiling joists to tie the walls together.

The key thing is that the ridge beam is strong enough to carry the roof alone and that those end girder trusses are properly sized yo carry the ridge beam. A local truss supplier can easily recreate this style of roof for you. Even with storage in the end trusses.

 

[Radix2]

I said in theory, because even though it has been perfectly sound all these years it is not a common building practice and the local building authority may not approve it as a replacement, especially it the additional height you want to add does NOT use that same construction technique (block and brick).

The reason this has worked is because of your thick walls !

If you are planning to raise the roof as one piece I would temporarily install rafter ties on the rafters that have none.

If it is correctly designed as I described above, the walls have nothing to do with it. And this detail is not all that uncommon. It is used often when you have a stairway/open landing in a truss room in a building to create the open space .

Girder trusses each side of the opening, a ridge beam between and rafters over the open space.

 

[Falcon67]

What they did is create trusses at each end of the garage to hold a ridge beam in the center - that is why you do not need ceiling joists to tie the walls together.

Maybe not. The old garage at our old house was built in the 50s. 16' x 22', all wood, 2x4 walls, 2x4 rafters, 2x4 ridge, 2x6 joists and only 5 joists - well, 3 if you don't count the ones with splits and cracks such that really weakened any power they might have had. It stood since the 60s most likely based on the construction and the style of the first layer of shingles. It's main issue was termite damage to the lower walls because it sat right on the dirt.

 

[the GOAT]

If it is correctly designed as I described above, the walls have nothing to do with it. And this detail is not all that uncommon. It is used often when you have a stairway/open landing in a truss room in a building to create the open space .

Girder trusses each side of the opening, a ridge beam between and rafters over the open space.

I kind of doubt that carpenters in the 40's building a garage were worried about sizing girder and structural ridge beams and making the proper connections.

More likely they left out the joists/ties in the middle and said good enough. Which apparently it was. But modern code enforcement officers don't like such reckoning.

 

[the GOAT]

I think the Goat meant the upper third on the collar ties.

I meant rafter ties/ceiling joists/floor joists in the lower third. Your right... Collar ties would have to be in the upper third to be effective. But I'm not sure code even requires them anymore.

 

[theoldwizard1]

What they did is create trusses at each end of the garage to hold a ridge beam in the center - that is why you do not need ceiling joists to tie the walls together.

The key thing is that the ridge beam is strong enough to carry the roof alone and that those end girder trusses are properly sized yo carry the ridge beam. A local truss supplier can easily recreate this style of roof for you. Even with storage in the end trusses.

That is a reasonable ASSUMPTION, but without close inspection that is all it is !

 

[75gmck25]

I appreciate the input, even though I tried to confuse everyone by calling the collar ties "chords".

This garage is too small to use for work on cars, but its solid brick and very useful as workshop area. If I tear down and rebuild it I would also have to comply with current rules for setback, non-permeable areas, etc., so I don't want to go in that direction.

What I would really like to do is lift the existing roof up as is, lay another course of block on top of the existing wall to increase the height, and then set the roof back in place. However, based on the roof design I'm not sure it will hold up to that. However, if I rebuild the roof I may have to just use new trusses to keep the building inspector happy for my permit. Its not really the cost of trusses that bothers me as much as losing that part of original design of the garage.

Has anyone tried raising an entire roof of this size up to get additional height? Mine is a small building and simple roof line, but its still a lot of mass to raise up evenly on each side as a single unit, and then keep it there while I add on to the side wall.

Thanks,

Bruce

 

[the GOAT]

Seems like it would be easier to just build a new roof with trusses.

you could always brace the roof and have a crane lift it off...buy/rent some cribbing and jacks...use a telehandler to lift it...shoring scaffolding might be strong enough....hire someone. Lots of options.

 

[theoldwizard1]

What I would really like to do is lift the existing roof up as is, lay another course of block on top of the existing wall to increase the height, and then set the roof back in place.

Reasonable.

Start by placing a rafter tie connecting each pair of rafter. They need to be level to each other. Use 2 doubled 2x6, on edge, under the new rafter ties and lift from each end of the 4x6. Once it is up in the air, it needs to be secured. Ratchet straps in an X, from the raised roof down to the walls. Wind is your enemy.

 

[Falcon67]

>Has anyone tried raising an entire roof of this size up to get additional height?

Review my work here - no cranes or any special/exotic equipment, just lumber and some floor jacks.

http://www.garagejournal.com/forum/showthread.php?t=41042

 

[rburke65]

There have been larger....heavier....items lifted but it will depend upon your ability and how comfortable you are taking on a project of this caliber. You can brace it and maybe lift it with a front loader and then brace. As said, watch the wind.