What's up with this roof?

[StoneHeartFarm]

Re: What\'s up with this roof?

Muhammad

Seeing your interior set up, I would expect moisture is a bigger culprit than heat. Do you know what kind of insulation was used? Foam or fiberglass? I've seen both. Foam is probably slightly more common around here. Basically, they laid the ceiling boards, glued foam to the backside and then nailed the sheeting directly to the foam, using long nails that would reach through and go into the trusses/rafters. There are usually at least some light rafters added above the finished ceiling for support for the roof sheathing. If moisture is building up in those nailer rafters, that could account for the ridge no matter how the sheating was installed, since wet pine has a pretty good expansion around its girth.

Also, have you determined yet that the roof is sheathed with plywood, or with something even more engineered like OSB (a very common material in this area)? OSB really doesn't like water and will crown along its edges fairly easily.

SHF

 

[Muhammad]

Re: What\'s up with this roof?

I'll double-check the plans when I get home, but AFAIK foam insulation was used (might have been more than one layer, or so I was told at one point), and the plans call for 1/2" plywood sheathing...

 

[dmccarty]

Re: What\'s up with this roof?

Muhammad,

That is one PRETTY ceiling. Exactly what I'm trying to get the
CFO to buy. /w3tcompact/icons/smile.gif

Other people are talking about venting the roof which is a
thing to look into. But it sounds like you have the shingles
on the plywood/OSB which in turn is on the rigid insulation.

The shingles need an airspace to moderate the temps.

If your shingles done have an airspace and you have
to redo the roof you may want to dig into designs on
how to accomplish this with rigid insulation.

This website, http:// [url]http://www.buildingscience.com/housesthatwork/cold/default.htm [/url]
has some design information. They sell some books that
provide design advice based on the "zone" you live in. The
books where HIGHLY recommended in a class I just took in
Solar House design. The books are not about building solar but
are about building energy efficient homes.

Here is the link to the books. A house located in NY would be
the book for Cold Climates. http:// [url]https://www.eeba.org/mall/builder_guides.asp [/url]

Another place to get roof info is http:// [url]http://www.jlconline.com [/url]. The site has
forums that I'm pretty sure had a discussion or two about roofs like yours.

Hope this helps...
Dan McCarty

 

[Argee]

Re: What\'s up with this roof?

Steve,
After seeing the interior, I agree that it's probably foam insulation. But I don't think the plywood is directly nailed through it. Reason being, the ridge vent. Whoever built it put those on to vent something. My guess is there's a 3/4 - 1" cleat nailed to the top of a rafter (sleeper) and the foam seats against this. Still if the eave vents are inadequate or plugged the sheathing will pucker. Could be a squirrels or wasp nest. The exposed sheathing has just plain gotta breathe.

 

[StoneHeartFarm]

Re: What\'s up with this roof?

Argee

Could be a lack of venting. But don't count on that roof vent to actually vent anything. I've seen more than one that has a ridge vent but no actual hole underneath it. I asked one contractor was he sure the ridge vent was installed right and he said "yah sure!" So I asked why there was no hole underneath. Shortly after a hole magically appeared.

It may be that something is plugged up, or that the plywood is simply reaching the end of it's useful lifespan (doubtful), or that there is some moisture penetration. Whatever has happened, it has gotten significantly worse over the recent wet seasons, and since the installation of the skylights. The skylights would certainly prevent venting between the rafters they are installed in. But would that be significant enough to cause other locations on the roof to also have problems?

What I'm wondering is what the span between cleats is. 16", 24" 48"? A 48" spacing might have been convenient. Over time, a little moisture and a little heat and the sheathing would start to sag, reducing the airflow through the vents and thereby accellerating the process.

SHF

 

[Hillbilly]

Re: What\'s up with this roof?

I have the same looking thing on my roof(not quite as significant),my roof is a 11/12 pitch.When we built the house a rain came and got the aspenite sheathing wet and it swelled on the edges(roof heave),this is a pressed 4 x8 sheet of roofing made out of chips pressed together in a glue,this stuff is good but does not stand the moisture as well as plywood.This sheathing we nailed to directly to the hand cut rafters(a rafter may even be a little high on my part).It is a little noticable,more so in the morning when a dew is on the shingles and the sun is hitting at a certain angle(the house was built in 1987)no leaks or anything.I would almost say Muhammad it is a moisture problem,I wonder about the ventilation,if it is not leaking and you can live with it I would not worry about the looks of it ,but I would go into the attic and see if the attic was sweating,or if there was a moisture problem ,if it was ventilation problem I would see about getting an electric vent that works off a thermostatic setting.Do you have any type of vents like a bathroom vent that could be perodically discharging air in to the attic that contains moisture?Strange it just started this past winter.

 

[MarkV]

Re: What\'s up with this roof?

Now I may well be missing something but as I look at the interior photos I am seeing a heavy structural truss with purlins on, I would guess, 4 foot centers. Normally in this configuration the finish ceiling is structural also and generally 2x6 tongue and groove cedar or pine material I my area. Muhammad says that foam insulation was used which is the norm on that kind of roof and the question becomes what is supporting the sheathing.

Over the years I have seen this done a number of different ways.

1. The sheathing is spiked through the foam and directly into the 2x6 structural ceiling. This would be the least desirable and leave no air space at all and no ridged support for the sheathing except for the foam. Some advocated this system years ago based on having a continuous insulation envelope.
2. Sheathing supports (non-structural rafters) are installed on 4’ centers to accommodate foam insulation cut for this spacing. This could or could not allow for an air space above the insulation depending on the size of the supports and thickness of the foam. That is a long span for ½ inch ply, even more so in snow country, and could be the problem even if “H” clips were used.
3. The preferred way around here is to use 2x6 supports on 2’ centers with 4” foam insulation in each bay. This leaves 1 ½” of vent space above the insulation.

Now why the joints of the plywood are not staggered is beyond me. That is a very basic building practice and I am sure contributes to the problem more than anything.

Muhammad, if you would like to do some easy investigating without calling someone in this is what I would suggest. Take a look at the skylights and tell us how much space there is from the glass to the finished ceiling. That will give us an idea as to how much space there is above the finished ceiling and if your plans show how much foam insulation was used we should be able to figure if the sheathing is directly on top of the foam. If you can get on that part of the roof and it is built like scenario #2, if there is air space below the sheathing, there will be some deflection in the sheathing when you walk on it. I would also try to see what can seen at the ridge vents. Some times you can see through or probe through with a coat hanger and get an idea if there is air space below the sheathing.

Now my last suggestion is we get MarkC over and have the Earthforce lift the whole dang thing up a foot so we can see what is going on. Then we throw some burgers on the grill and come up with a fix./w3tcompact/icons/smile.gif

MarkV

 

[Inspector507]

Re: What\'s up with this roof?

Mark,
From the looks of it, I'm not sure the whole gang is gonna stay up there for long. We'd be getting brewskis out of the fridge without climbing down /w3tcompact/icons/laugh.gif.

 

[Muhammad]

Re: What\'s up with this roof?

Mark,

Thanks for the comments. I have found out some more about what should be up there:

1" tongue & groove finish ceiling boards
Rigid foam insulation
1x3" 16" OC vertical slats (I suppose spiked into the ceiling boards?)
1/2" plywood sheathing attached to the 1x3's...

There's a good 4-5" where the skylights are, but I will get up there to see if I can confirm the suspected method used.

Still doesn't explain why the vents don't run across the entire peak.

 

[WVBill]

Re: What\'s up with this roof?

Muhammad:
<font color=blue>1x3" 16" OC vertical slats (I suppose spiked into the ceiling boards?)</font color=blue>

I hope your 1 X 3 vertical slats are spiked through the rigid foam and into the horizontal purlin structural beams underneath your ceiling boards and not just into the ceiling boards. If it's just into the ceiling boards then you've got only about 3/4" of nail length holding your entire roof onto the house (assuming they're not sticking through the inside of your 1 x ceiling boards).

Whether they are or not, what you describe would only give 3/4" air space between the plywood sheathing and the rigid insulation which doesn't seem enough to me.