Roof structure

I inspected a home built in 1973 - heres a picture of the roofing structure, i have not come across this type yet. ( I get lots of housing boom bungalows)

What type of roof structure construction is this?

Any Inherent concerns with this type specifically?

Any tips? resources?

Built on site trusses.

I have no idea if they were done according to a plan.

Any sagging at the middle?

Here is a previous discussion.

Thank you Mr Larson,

So its looks like a conventional field built (site built) truss - i have no verification of it being an engineer designed or approved construction. I will advise client not to attempt to modify it and that it is highly recommended to have an engineer evaluate it.
However, i will say here that there was a load of snow on it and it didn’t seem to be sagging at all.

I agree with the others. Like mentioned look for sags in the rafters. There isn’t much pitch to that roof so it would probably more likely visible with a lot of snow. Always check that those plywood gussets are attached well and none are missing.

If that’s 1/2" plywood and those rafters are more than 24" OC, the plywood is overspanned.

Leaks at the ridge, especially long-term leaks bad enough to soak the plywood gussets but not be visible from inside the home, can weaken gussets over time. Look for staining or decay indicating leakage.

Gussets are sound building build practice for furniture building .
1: No ridge beam and span is 4-8 feet? . Still over sized
2: Look at nails. Some are starting to transfer rust staining on to sheathing, meaning
a>there is a humanity problem but not evident on all nails.
b>Shingles are nearing there life span and or lack of under-layment at one time or now.
3: over spanned.
4: question the gable venting louvers being over-sized. Might allow weather to enter on windy days.
Any decking that widely spanned would need to be 1 to 5/4 ply.

Without seeing the stamp on the plywood we can’t say it’s over spanned, but 3/8" plywood with H clips is common even on 24" in older homes.

Those spans are over 24’. Clips are bylaw-ed now. 3/4 decking on thet roof would fail prematurely in my opinion.


How do you know the spans are exceeding 24"? With this truss design, it appears that the center vertical web support must be placed over a load bearing wall.

Well only Joseph can tell us the span or the thickness of the plywood. 3/4" plywood can span 48" with edge support and 36" without.

Robert E.
look at the nail patterns for the shingles.In the roof decking.
4 nails horizontally equals 3 feet.
4 nails per single.

It was acceptable in many places for a while.

Built in 1973 ! Nearly 40 yrs. , I would say they where well engineered , and proven ! Probably stronger than todays engineered ! ;):D:D

Yes Allin I agree . It was well engineered even if, or if not, by and architect.