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Old 11-11-2013, 09:29 AM   #1
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rerplace roof on 200 year old house


We have a 210 years old stone house with the original rafters and perlins. The house is 45 feet long and 20 feet wide and is two stories high. The roof has a straight ridgeline--nothing fancy. Two chimneys protrude through the roof.
The front of the roof has individual metal shingles probably at least 50 years old. The back of the roof is standing seam metal. We never had sweating problems with the roof until we put tight, insulated windows and doors in this place and now we get some condensation on the under side of the roof just in really damp, cool weather. There are no vents in the roof though there is an 18 in by 18 inch window at one end of the house that I have removed and placed a 16 inch fan in. There are a lot of openings in the roof around the edges--many places there is a half inch gap I can see light through. In other words, the roof has a lot of room to breathe. There was a vapor barrier placed on the roof but it has dried out and deteriorated and is falling like rain in the attic.
The roof does not leak but we want to have a new roof put on and it appears from talking to roofers that this will be very complicated for many reasons. For one thing, the rafters are not standard in any way. Most of them are 3 and a half inches wide by 4 inches high. But there is some variation there. Most of the rafters are spaced about 26 inches but one space is 40 inches. The perlins are a full inch thick and average about 2 to 2.5 inches wide. They are spaced about 1 to 1.5 inches apart. The rafters are 13 feet long and from floor to the peak of the roof is 7 ft 6 inches. One major problem is that the rafters have sagged about 2 to 2.5 inches at the center.
I have talked to many roof contractors and have gotten a great variety of opinions about how to handle this. Some say I should pull off the entire roof and start over. I hesitate to do that as I like to preserve the history of the place. At the peak where the rafters meet they are slotted and have a wood pin to hold them in place.
Some contractors said we should pull off the metal, place vapor barrier on the perlins and put new metal over it. We want to do a standing metal roof as would be appropriate to the era this house was built--1804 ( the original roof was probably wood shingle but we don't want to get that route).
some contractors say we should pull off the metal, sheet the roof, apply vapor barrier then put the metal on that. Some say to screw 2x6's against the existing rafters for strength then go from there. Some say we can't apply standing seam with a 2 inch sag in the roof. We are in central Pennsylvania.
Any suggesting would be greatly appreciated.

Fred

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Old 11-11-2013, 10:16 AM   #2
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rerplace roof on 200 year old house


Got some pictures inside and out?
If the roof sagged that much then it was under built to begin with.
Adding more anything over a substandard roof structure is sure not going to help.
Sometimes you just have to bite the bullet and start over to do it right.
And there right, standing seam can not be bent to fit.
If your getting that much condensation I'd be adding soffit vents and gable end vents or better yet a ridge vent, air sealing the attic, adding the proper amount of insulation.
If there's no soffit vents any roof or gable venting is going to do much.

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Old 11-11-2013, 11:10 AM   #3
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rerplace roof on 200 year old house


Thanks for the reply. Here are some pictures I took inside the roof. As you can see in the one picture, I ran a 2x3 from the center of each rafter to the floor (or joist) to give the rafter some support at the center. This was recommended by a contractor friend. You can see the gaps in the roofing in the last picture. You can also see some mold that grew on the perlins(if that is what they are called). I sprayed some Clorox solution on the mold to kill it.
The gap in the rafter joint in picture 2 shows the result of the rafters sagging.
The rafters are probably hand cut and of inconsistent size and spacing. It appears that if they put in a larger rafter, they made the spacing between the rafters larger--economy of wood use I guess.

Fred
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rerplace roof on 200 year old house-perlins-4.jpg   rerplace roof on 200 year old house-rafter-1.jpg   rerplace roof on 200 year old house-rafter-supports-2.jpg   rerplace roof on 200 year old house-roof1.jpg   rerplace roof on 200 year old house-roof6.jpg  

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Old 11-14-2013, 11:06 AM   #4
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rerplace roof on 200 year old house


The condensation is due to the attic being hotter and more humid than the exterior. The same problem probably existed before you put the windows in, but was mitigated somewhat by the underlay (the material you are calling the 'vapour barrier'). This can be fixed by installing more ventilation and sealing off the attic space from the house. Venting can be done either at the gable ends or at the ridge and soffit, although soffit venting may be difficult because of the way the roof is built. Seal any penetrations in the ceiling (holes, lights, etc) to stop warm moist air from entering the attic space from the house.

It's not unusual for a roof of that age to sag, but something needs to be done in order to get another 200 years out of the roof. Replacing the trusses is fairly major and I agree, it would be a shame to toss those nice pinned beams. Personally I would remove everything but the existing rafters, sister new rafters to the existing, and apply new strapping (or sheathing), underlay, and metal roofing.
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Old 11-14-2013, 11:28 AM   #5
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rerplace roof on 200 year old house


Thanks!! That is the best idea I have heard yet. That sounds like a winner. I appreciate that.
One concern I have about that is that the spacing of the rafters does not come out to the length of any sheeting material--the rafter spacing is a bit more than 24 inches. Any idea how to deal with that? One 4x8 sheet would cover only 3 rafter spaces. That would produce a lot of waste, but I guess I will just have to live with that. Or, could I run 2by4's across the rafters at 2 foot intervals and screw the sheeting to that?

Fred
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Old 11-14-2013, 02:46 PM   #6
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rerplace roof on 200 year old house


Quote:
Originally Posted by newroof View Post
Thanks!! That is the best idea I have heard yet. That sounds like a winner. I appreciate that.
One concern I have about that is that the spacing of the rafters does not come out to the length of any sheeting material--the rafter spacing is a bit more than 24 inches. Any idea how to deal with that? One 4x8 sheet would cover only 3 rafter spaces. That would produce a lot of waste, but I guess I will just have to live with that. Or, could I run 2by4's across the rafters at 2 foot intervals and screw the sheeting to that?

Fred
You might just need to cut a little off each piece. Otherwise, you could add another rafter (in between the old ones). Personally, I'd just cut the sheathing to make it fit. 200 years ago they didn't think about material being 4x8', which is why you see 1x material run at different lengths perpendicular to the rafters..they used what was available.
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Old 11-14-2013, 03:11 PM   #7
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rerplace roof on 200 year old house


Can you see what's happening? That 200 + year old house is groaning with every step you've taken beginning with the windows. You can take the windows etc. back out to square one, put an original wood shingle roof on and it will last another 200 years. OR you can continue to attempt bring it up to someone's code according to FHB etc. etc. and in about 20 years all that will be standing will be the rock walls (maybe).

Attempting to air seal that structure would be like trying to push a chain and to my knowledge it hasn't ever been successful.
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Old 11-24-2013, 06:23 PM   #8
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rerplace roof on 200 year old house


Quote:
Originally Posted by newroof View Post
Thanks!! That is the best idea I have heard yet. That sounds like a winner. I appreciate that.
One concern I have about that is that the spacing of the rafters does not come out to the length of any sheeting material--the rafter spacing is a bit more than 24 inches. Any idea how to deal with that? One 4x8 sheet would cover only 3 rafter spaces. That would produce a lot of waste, but I guess I will just have to live with that. Or, could I run 2by4's across the rafters at 2 foot intervals and screw the sheeting to that?

Fred
I had to replace the roof on my house 15 years ago. It's not as old as your house, but it was locally milled off our property 100+ years ago. The rafter spacing was close to every 24 inches and some of the rafters (true 2x6s) were sagging.
I sistered 2x6s to the sagging rafters. I put down 4x8 sheets of plywood on top of the purlins and shingled on top of that. I put in a ridge vent, gable vents, and soffit vents.
The roof has served us well, and we got to keep the original wood.
If I can answer any questions for you, let me know.

BG

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