sheathing change & trusses

[SGKent]

live in a tract home built in 1979. Roof trusses are 24" on center and 3/8" roof sheathing (plywood). Getting ready to spec a new roof as the old one is now 24 years old and showing age. Fiberglass comp 3 tab.

In 2001 put in a whole house fan and had to cut a truss. City required an engineer's stamp on the modification. The CE who did the work looked at it as part of the process and he mentioned that the roof was not designed to hold much more weight than was on it just in case I ever wanted to go to a heavier tile. I have tried to locate him, and also have written a friend who has CEs working for him on commercial projects to see if he knows anyone who does freelance work here in the Sacramento area. My goal is to either add an additional 3/8" to the roof plywood, or replace it with something more robust. I don't know if the trusses will handle the weight and there is no way to find the original truss loads with the house being 40 years old this year.

Anyone have alternative solutions on how to find an answer to the question of whether existing trusses will handle heavier plywood? Also, while I have no plans for solar now because of the return on investment, if at some future time the cost came down I might consider that too. And that is additional weight.

Last - once I have the answers, would it be easier to hire a GC to handle all the work?

 

[strutaeng]

I think I asked in another of your threads, but can't remember, is it 3 tab asphalt shingles or tile roof? Did you have tile at some point?

3 tab weigh about 2 psf ( conservatively), while tile can weight between 6 to 10 psf, depending on type.

Are your trusses the type that have plywood gussets? I think the metal plated trusses you see today came along in the 80s.

If the engineer did not do calculations, I can't see why he would speculate the weight was higher than designed.

I can't see how adding another 3/8" plywood would cause any problems. How are your deflections? Any visible (gross) sags?

Around here roofers do this kind of work, maybe a carpenter. A GC would be too expensive for just coordinating 2 trades.

 

[Kaizen]

Truss manufacturers are not very open to staying anything. Hire a structural engineer to assess the design of the trusses. He can also tell you how to fix the cut one. Half inch ply or zip panels added should not affect the weight much. The shingles sure will though.


Sent from my iPhone using Tapatalk

 

[ekimneirbo]

Are the trusses you currently have sagging ? Trusses are supposed to be designed to handle snow loads (even in California ?), so I have my doubts that you need any repairs. When new shingles are put on, the contractor should remove the present ones, so the load on your roof should be about the same. You could always go with a metal roof. They can look really nice. Also, depending on the size of the building, if weight is a problem, you could run a beam under the trusses and set it on a pole at each wall.
Removing a whole roof is an expensive proposition. There are a lot of houses with roofs 40 years old and they don't need new trusses. Unless they are sagging, I wouldn't think you need new ones either. My house is 40 years old this year and the trusses are just fine.....and we have had up to 17" snow loads on them.

 

[SGKent]

original was 20 year asphalt comp. Ones on it now were put on in 1996 after a tear off. 3 tab fiberglass comp. Starting to look mostly fiberglass as the small embedded stones have washed away over a good percentage of each shingle. I never would have thought about the weight except when the civil engineer looked around at the attic on the inside before designing how to change the truss I had to cut to clear the whole house fan said as I recall, "somewhat under designed truss system. Is fine for the load on it now but don't add much weight to it, it is pretty much at the limit now. Just in case you ever think of going to a heavier composition tile. You would have to add additional bracing." I said something like it has 25 year on it now, he said something like "probably good to stop there and not go to anything like a 30 or 40 year. Solid tiles are definitely out."

There is only one roof on it. There is no deflection from the view but when you walk on it, it is pretty springy, and if one isn't careful you can hear the wood or paper break a little under foot. 3/8" doesn't even meet code anymore except grandfathered in. I think 7/16 is the min - although it is only 1/16" more. Lots of articles say that with 24" on center 5/8" should be the minimum. That would require adding 1/4" sheets to it and almost double the load. I've got a letter I wrote to him for advise but who knows if he still does that kind of work. According to google he is a project construction manager for a big development firm here in central California now. I also asked a friend in surveying who has civil engineers on his staff if he knows of anyone - but the guys who work for him do mostly commercial stuff associated with land development and surveying.

 

[matt_i]

Pics of your understructure and roof pitch would be helpful.

I will say that just adding plywood to plywood and nailing off the edges isn't the same as the equivalent thickness because of the additional shear that can be developed on the neutral axis because of the full-glueup of the thick single sheet...fancy way of saying it gets stiffer.

You can approximate that by gunning your own construction adhesive into wavy patterns before laminating sheets but over a whole roof it will add up to a lot of tubes.

Re: the contractor, there is forevermore the (good, fast, cheap) conundrum where you pick two. Contracting it will be fast...but after that....

 

[Handyfarmer]

how wide is the house, or how wide are the trusses, and what is the cord size, (bottom board), are there walls in the house that run in the same direction of the truss supporting walls, or is it open from one out side wall to the other out side wall?

with out some more info, difficult to even guess to what extend the trusses are loaded, or if there is "extra" in the design,

extra in side walls, will help support the truss, (not the design of the truss) but it will help, and the wider the house is most likely nearer the max of the truss in design, the bottom cord being a 2x4 or a 2x6, makes a difference,

 

[SGKent]

how wide is the house, or how wide are the trusses, and what is the cord size, (bottom board), are there walls in the house that run in the same direction of the truss supporting walls, or is it open from one out side wall to the other out side wall?

with out some more info, difficult to even guess to what extend the trusses are loaded, or if there is "extra" in the design,

extra in side walls, will help support the truss, (not the design of the truss) but it will help, and the wider the house is most likely nearer the max of the truss in design, the bottom cord being a 2x4 or a 2x6, makes a difference,

looking at truss designs it is a common truss. The house is 35' wide center to center with a bearing wall down the middle more or less (13.5' from front side, 21.5' from back side) except where crossing a hall way. 2x4 construction and trusses, probably douglas fir. The garage is attached and has a width of 19'. Where the house transitions to the garage there is a cantilever section of about 8 or 9 feet that ends at each garage wall and holds up the house side of the garage roof where it transitions to the house. As I recall, there is a double top plate over the bearing wall and another sitting under the center of the truss that loads on other walls so that the bottom of the truss is supported at roughly 13' and then 5' away again at 22' from the back side of the house.

Here is a copy of the drawing done by the engineer to make changes for a whole house fan where I had to cut a diagonal (on the front side of the house). The red lines are the original truss layout and exist on all but the one truss cut to accommodate the whole house fan. Trusses are 24" OC

View media item 95733
House:
View media item 95732
Red is center, and double 2x4 under trusses. Blue is bearing wall with double 2x4 top plate. Green is direction of trusses.
View media item 95734

 

[matt_i]

I was interested, going to 1/2 cdx adds about 0.2 psf per tables on the 'net and going to architectural shingles is ~ 0.8psf increase (2.2 to 3psf).

So you'd gain about 1psf doing both upgrades. I think you could save 0.1 to 0.3psf if you switched from the old felt paper (tar paper) to a synthetic woven underlayment (I have Grace Tri-Flex in my head as I write this).

If there were to be a double layer of shingles...not saying there is, but if you did find that you'd know that with a tear-off you would be in better shape.

Another possibility is to get a quote and a drawing of a new 4:12 or 5:12 pitch truss (same dimensions as existing) note for architectural shingles and see how differently it is constructed relative to yours.

If I drove by that house here in MI I wouldn't ever think twice about putting architectural shingles on it, of course ~25 psf snow loads are designed-in here...so the addition of 1.0psf would be very low.

 

[aar_man]

As the PE did work for you before, his seal with name and license number should be on the drawing. Take his License number/name and log into the CA Department of Consumer Affairs, select Professional engineer. In PA, it gives you his/her current city and if the license is active.

 

[PugetDude]

Replace the 3/8" sheathing with 5/8", gun-nail with 2" screw-shank nails at about 6" OC.
The roof will be stiffer than a honeymoon *****.
Use 30# felt, then a 30-year 3-tab.
It will last your lifetime.

I suspect the engineers comments were more about the flimsy 3/8" sheathing than the trusses.

Good Luck.

 

[SGKent]

Replace the 3/8" sheathing with 5/8", gun-nail with 2" screw-shank nails at about 6" OC.
The roof will be stiffer than a honeymoon *****.
Use 30# felt, then a 30-year 3-tab.
It will last your lifetime.

I suspect the engineers comments were more about the flimsy 3/8" sheathing than the trusses.

Good Luck.

I suspect so too.

As the PE did work for you before, his seal with name and license number should be on the drawing. Take his License number/name and log into the CA Department of Consumer Affairs, select Professional engineer. In PA, it gives you his/her current city and if the license is active.

Thought of that one already and mailed a letter to him over the weekend at the address the state has for him. Hopefully he will reply, and still take on freelance work. I am hoping he will approve of just upgrading to 5/8" from the 3/8" and no changes to the trusses. The shingles are one layer and look like this:

As I recall they are Elk, now GAF-ELK

View media item 95739
View media item 95740

 

[ekimneirbo]

If your roof has lasted this long with no problems, I would just leave it alone. A lot of these home inspectors and engineers just want to "cover their a**" and worry you with a lot of talk. The house looks great and if you aren't having a problem after 40 years, its pretty well proven itself. Check your insurance policy and make sure the roof is covered for any possible "hail damage" or snow load or other misfortune. Then tear the shingles off and replace as usual. My son bought and sold several homes after he got out of the military till he finally found his dream home. Every time he bought or sold one, the inspectors would always find some flaw that needed repair and co-incidentally they always had a buddy that did that kind of repair work.
One said there was too much moisture in the crawl space and he had to use a guage to detect it. Wasn't standing water or mud, just what was in the air and one small area where a little water drained thru. Wanted about $4000 for his buddy to come spray rock in the crawl space. Funny thing was when he bought each house the previous inspectors had no problem. Pretty much a lot of them are always looking for ways to scam people...legally. I'd stick with what you have and quit worrying about it. If your neighbors have houses built at the same time by the same builder, why aren't they having any problems. I'd think long and hard before expending that kind of money if you don't have a serious problem with sagging or leaking.

 

[SGKent]

If your roof has lasted this long with no problems, I would just leave it alone. A lot of these home inspectors and engineers just want to "cover their a**" and worry you with a lot of talk. The house looks great and if you aren't having a problem after 40 years, its pretty well proven itself. Check your insurance policy and make sure the roof is covered for any possible "hail damage" or snow load or other misfortune. Then tear the shingles off and replace as usual. My son bought and sold several homes after he got out of the military till he finally found his dream home. Every time he bought or sold one, the inspectors would always find some flaw that needed repair and co-incidentally they always had a buddy that did that kind of repair work.
One said there was too much moisture in the crawl space and he had to use a guage to detect it. Wasn't standing water or mud, just what was in the air and one small area where a little water drained thru. Wanted about $4000 for his buddy to come spray rock in the crawl space. Funny thing was when he bought each house the previous inspectors had no problem. Pretty much a lot of them are always looking for ways to scam people...legally. I'd stick with what you have and quit worrying about it. If your neighbors have houses built at the same time by the same builder, why aren't they having any problems. I'd think long and hard before expending that kind of money if you don't have a serious problem with sagging or leaking.

all valid points. In 1996 I spoke with one of my younger brothers who knows roofs. He started in residential, commercial, factories, colleges, Dept of Defense stuff, and now he runs roofing and decking in high rise buildings all over the west coast for a major company. He is the one who suggested 3/8" is too thin. He suggested throwing an additional 3/8" on it but that was 25 years ago and the roof has sagged and aged a little since then. Sacramento is not near a major fault but there have been earthquakes within range that did some damage historically. He suggested that with a stiffer roof the house would fare far better if we have an earthquake. The earthquake insurance here is useless - they cover 80% of the damage after like a $20,000 deductible - and anything masonry is not covered at all. It is the same policy all over California so we pay a higher rate so people in SoCal and the Bay Area can have lower rates. So if you have foundation issues or the chimney falls into the house then they don't cover anything because the foundation or chimney failure is the cause of the other damage. Just like if you flood because of a hurricane, or a tree blows over in it onto your house, but you don't have hurricane insurance then you are SOL. That is why you see so many fires during hurricanes. It becomes impossible to say that the hurricane started the fire so the fire ins ends up paying. Kinda like we ran off before the hurricane and forgot to turn off the stove, or there was a candle we forgot that was burning in the bedroom ... .

 

[Handyfarmer]

I would strip it down to the current sheeting and sheat over with 1/2 or 5/8 leaving the 3/8 under it, I am no engineer, but have been building for over 40 years, and with that center wall down the middle I am sure you will not have any problems, the trusses were designed to clear span, and with a center wall, it most likely triples the load carrying capacity of the truss, and since the truss has a (i will call it a king stud) in the center of the truss weight is being transferred to the center wall, and the way the truss is designed it is like having two short truss built in to one,

I have a 24 wide building with only 2x4 rafters and a ridge board, and it was moved once in its lift, and was built in the 1920's, yes there is a bit of sag in its roof, but it is only 90+ years old, what I am trying to say is I do not see any problems,

 

[SGKent]

from a google photo it looks like the roof is 4:12. I will actually measure in the morning. Also sent an e-mail to the county to see if they have copies of original plans from when the permits were pulled for this tract. Maybe some truss info will be there if they have plans on file. Mailed the letter to the Civil Engineer this morning seeing if he is interested in taking a look at it. Not much else I can do until someone who designs trusses tells me that these can handle going from 3/8 to 5/8. The roof and garage is 70 - 75 sheets of 4x8 plywood so multiply that times 20 lbs difference per sheet, and it adds up to about 1500 lbs over the whole roof. This area is not one of my areas of expertise.

All that said - thank y'all for the suggestions. I think that the trusses will be Ok doing this but the builder cut so many corners that I don't know. About 5 years ago I replaced the interior door to the garage with a much better one. When I took the old one out the frame was held in by only one (1) nail, and the trim molding. No wonder it shook each time it closed. It had vibrated itself to pieces over the years. Pulled the first nail (only one unbeknownst to me) and almost got clobbered by the heavy door as it toppled at me.

Worst case is I'll never get a definitive answer, and the roof will be replaced on the existing 3/8th sheathing again.

Steve

 

[SGKent]

I happened to ask the city building dept if they had any local civil engineers who they refer to and the head engineer down there wrote me back and said 5/8" cdx will work fine for these homes. Nothing special needs to be done. Guess it is time to call the roofer and get a bid.

 

[theoldwizard1]

Replace the 3/8" sheathing with 5/8", gun-nail with 2" screw-shank nails at about 6" OC.
The roof will be stiffer than a honeymoon *****.
Use 30# felt, then a 30-year 3-tab.
It will last your lifetime.

I suspect the engineers comments were more about the flimsy 3/8" sheathing than the trusses.

Second !

 

[KenC]

Add a layer of 7/16" or replace the 3/8 with 5/8? IMO either will work well for you. But, it is going to be a lot more labor to replace, more expense in material and added disposal fees.

On my house, given those choices, I'd add a layer of 7/16 OSB, nailed with 8 penny gun nails, 6" on the edges, 8" in the field.

 

[SGKent]

got a hold of the engineer who told me about the truss issue - he said he remembered the home and that his concern was more if a heavy duty architectural shingle was used with overlay, or a tile roof was added. Did some calculations and said the 7/16" OSB overlay would be Ok but nothing more. Roof is done. They put down 7/16" OSB overlay and GAF- Elk Timberline HD reflective series.