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weng19 03-04-2008 01:28 PM

Help with ventilation of Gambrel Roof

Great forum and I am learning a lot already. I would appreciate any and all advice you all may have regarding ventilating and insulating my dutch colonial's gambrel roof.

We live in suburban DC in a 2-story dutch colonial and have a 1000 sq ft attic. The roof itself has 1 gable vent on each side and an attic fan. There are no soffits, and there is about 6 inches of cellulose blown in. Being a gambrel roof, the roof slopes sharply downwards to cover the entire second story.

I am trying to :

1. Improve insulation: the second story is much colder than the first story during the winter and I am trying to fix that.
2. Improve attic ventilation: we have cedar shake shingles and I am trying to prolong their life.

I've replaced recessed lighting to insulation compatible fixtures, and am about to blow-in 24 more inches of cellulose. I stapled 4ft polystyrene baffles to the rafter/joist intersections.

I had anticipated going between every other rafter and installing 16" x 8" undereave vents (about 20 total, front and back side of roof).

However, is this a good idea? Specifically:

1. Will air travel through the soffit, through a 2 ft wide x 10ft channel (i.e. the second story) and into the attic?

2. If yes, is this a good thing for insulation? My second story walls are cold during the wintertime already -- so I don't think there is much (any?) insulation in them to start with.

I ask for help -- I had one handyman come out and see -- he said no to questions 1 & 2, and said to just blow insulation into the space between the second story roof/wall, as well as the roof. Regarding ventilation, he basically said gambrels are tough to ventilate.

Any advice would be appreciated, thanks!


travelover 03-04-2008 01:48 PM

Does this help?

inspectorD 03-04-2008 03:09 PM

Travelover, your link kicked me off the computer...:confused:

Welcome aboard..the ventilation needs to be there for the roof.
The gambrel is basically a sloped wall with shingles on it. In your case..a wood roof. This gets more complicated. If you want to save the roof , it needs to ventilate to dry. You may have insulation in there already which was installed incorrectly against the bottom of the roof deck or shingles.
If your shingles are curling towards the centers, this is why.
The underside of the shingles will also start to decay.
You don't need a handyman, you need a professional contractor out there to give you some real, up front advice. This gets tricky with these types of roofs.
Any good roofer who installs alot of wood roofs will also be able to give you some great advice.
Post some pictures and get someone there to take in the entire issue. Then tell us what the solutions could be...and we will try to tell you if they are selling you a boat with a hole in it...the best we can.:)

travelover 03-04-2008 04:26 PM


Originally Posted by inspectorD (Post 16621)
Travelover, your link kicked me off the computer...:confused: ....................................

Not sure why, it is a PDF file, but works OK on my computer.

weng19 03-04-2008 05:39 PM

Thanks...Plan made
Thanks traveller for the pdf. The pdf basically hedges, I think -- it states in the retrofit section that you MAY want to blow in insulation, but you also want to preserve ventilation. And it points out the mansard part doesn't need ventilation.

A couple facts: I don't have condensation/ice dam issues. And (unfortunately) I do not have existing soffits where the roof meets the steeper mansard. There just isn't an overhang to install them.

I spoke with my inspector and a roof guy who knows my house. Both guys recommended to NOT blow insulation into the mansard part of the roof, but just keep the 4 ft baffles in place as I have them (installed where the mansard meets the roof), and blow-in insulation in the attic.

My plan is to
1) blow in insulation into the attic
2) see if it makes a difference
3) if it continues to be cold on my second floor, then I'll get some infrared photos to see where the thermal break is. If it's at the junction of the mansard and the roof, I'll consider blowing in insulation into the mansard part of the roof.

Regarding ventilation, I think I'm at a loss as far as options go, short of redoing the entire roof structure. It sounds like soffits on the under eaves is silly; and I can't do ridge vents or add soffits where the mansard meets the roof as there isn't an overhang.

My inspector says 2 gable vents & 1 attic fan are decent ventilation for a 1000 sq ft attic. (The gable vents are ~8 sq ft total). My roof installer says that is woefully inadequate. Although they disagree, I still think that I don't have any options to improve it, short of redoing the entire roof -- both of them agree on that.

That's the plan! Will check back for posts, and will reply after a couple weeks with the new insulation. (going from 5 in cellulose to abour 24 inches).



inspectorD 03-04-2008 06:40 PM

Sounds good
Try this link for more info on your type of roof.

The guys you talked to are pretty close in the advice, read some more for your own piece of mind.
Sounds like you have it covered, good luck.:)

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