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Small Cabin Forum / Cabin Construction / Insulating a vaulted ceiling sans ventilation
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# Posted: 24 Oct 2021 06:38

For years the construction industry has built homes without insulation or roof ventilation. We’ve since learned and been taught to insulate (duh) and ventilate.

One of the first projects I need to tackle on my soon to be mine cabin is the roof structure/insulation. I was suppose to close on the house Friday but the sellers RE attorney dropped the ball and I’m stuck here waiting and thinking some more about what needs to be done.

That said, the cabin has a full width enclosed porch on one side of the Eve and a partial width enclosed porch on the other side. Regardless of the cabin not having soffits either, it leaves little place to even add a vent for the roof structure. There’s also no ridge vent.

I know running insulation up to the sheathing can create a “hot roof” and NJ isn’t say Florida or Texas but we still get pretty warm up here in summer months.

M question is this: how do I add ventilation above the insulation where the rafters end into a porch? Am I ok leaving an air gap with no vents?

I kind of understand the importance of venting a roof but is it completely necessary?

The current roof is a handful of years old and will probably need a re-shingle in a few years. I was thinking that’s when I could have someone install a ridge vent. Although, Hopefully by then I’d have my interior insulated and ceilings finished.

Just looking for some thoughts and ideas from the group. I’m a firm believer that just because someone says “it must be this way or else…” there isn’t a different way to achieve a similar result. Guess that’s why I wanted to buy a cabin: it’s not like any traditional stick-framed house. Everything is unique.

Thanks Much!

# Posted: 25 Oct 2021 20:29

You won't be able to add a functioning roof ventilation system without paying a lot of money. Adding only one component (just a ridge vent, for example) would be a waste of time and money because you still wouldn't have a functioning system.

There are situations when you can go without ventilation, yes.
Because you appear to have a cathedral ceiling, your best option is to spray-foam the underside of your roof. You could do fiberglass-batt insulation instead, which would be cheaper, but you'll have to seal it up tight to keep warm (moist) interior air from escaping through the insulation.

# Posted: 25 Oct 2021 21:06

Are you thinking primarily ventilation in the hot months? If so, here is what we have and what worked quite well last summer (our 2nd summer at this place).
It is a rough, sawmill board cabin, 16x24ish, cath ceiling over 1 big room. Not air-tight at all, some sloppy bat and rigid foam odds & ends insulation. The ceiling is bat up to the peak, boarded over except for the peak which is still open, uninsulated; I expect it 'breaths a bit'. Boards over rafters/purlins, metal roofing.
The first summer, 2020, the heat 'stacked' horribly, even with the door and all windows open. Come winter, the then woodstove drafted poorly (thru the gable end wall stovepipe), any heat went up into the peak. I learned to run a small fan to circulate the room air to kick the heat back down and about us. Big win, that.
Come spring I had decided not to install an up thru the roof new chimney (we went with an LP furnace, another big win); looking at that high up hole thru the gable wall I thought 'vent?'. I ran a 6" stovepipe out horizontally, put a screened cap on outside, put a 'belled' 6" to 10" inside (to 'funnel') and a small fan pointed at it. This simple 'power vent' worked great!
I will refine it better now that we have a proof of concept season behind us.

# Posted: 26 Oct 2021 07:09

You may be reading too much into the term "hot roof". one link example from Hot Roof :

Unfortunately, the term hot-roof is a misnomer as the roof really is not that much hotter than a normal roof. Most studies show anywhere from 1° to 5° maximum increase in surface temperature during the sunniest part of the day, while at night the surface temperature drops faster than a regularly vented roof. A hot-roof is one where there is no ventilation required as the insulation is directly attached to the roof sheathing.

As Spencerin suggests, assuming your budget can handle it, proper spray foam may be the best approach as using any other insulation depends on a really good seal which is harder to do than most think. Just make sure the company spraying uses the correct foam type.

With a very high open cathedral ceiling in our cabin I had it sprayed (including the end walls upstairs) and it was not as expensive as I originally budgeted, it was fast, efficient and does a great job.

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