[dcobbett]

Hi there, I'm hoping to get some professional advice on a roofing issue. I'm a medium level DIYer, comfortable doing things myself if I know I'm doing it the correct way. With roofing, I'm approaching it carefully bc the last thing I want is a leaky roof. So I AM getting estimates from roofing contractors for this work, but I'm also researching how to do it myself in case I decide to go that route.

Here's what I need to do...

I'm renovating my kitchen and installing a vented range hood, but there is an old vent in the roof which I will no longer need, it's in the wrong place to use for the new range hood. There is a roof cap on the flat tar and gravel roof. It has never leaked so I'm thinking I should just leave that so as not to risk creating a leak. But I do want to close up the interior of the hole, so I can put insulation and drywall over it. I want to make sure the hole is sealed against moisture so I'm not getting wetness into my insulation and behind my drywall.

Because of the roof cap I can't access the opening from the top, so I'd have to close up the hole from underneath, making it tricky to make sure it's sealed and no water is able to sneak through. However, because the cap seems solid and has never leaked, maybe I don't need to worry too much. Please let me know if you have any ideas.

In the pics you will see there is a square metal vent pipe sticking through the hole below the roof cap. This 'pipe' is in loosely and I could pull it out, it's not sealed into the roof or roof cap.

Thanks!
Dan

 

[de-nagorg]

Is that curved cap on the outside part of the square loose extension inside?

If so I would just take the thing out, shorten the extension, then replace it where it was and screw it to the inside somehow to prevent it from blowing off in a windstorm.

You say that this is not leaking anywhere, and leaving it in place gives you a little attic ventilation to release any summertime heat buildup.

As well as saving the money and time of re roofing that area .


ED

 

[dcobbett]

Hi de-nagorg. Yes, that curved cap on the roof is covering the square loose extension on the inside.

I should clarify that it's a flat roof with a cathedral ceiling, so there's no attic, just 2x8 rafters with the roof on top and drywall below.

Sounds like you're not too worried about the exposure to air and potential moisture so you think leaving it open is ok. That would certainly be an easy way to go. It doesn't rain a lot here but we do get moist air from fog and some rain during the winter. Thanks for the reply!

 

[Bud9051]

Sounds like you have no ventilation, you must be in a southern climate zone. You do mention winter so tell us where you are.

In general, the space between the inside ceiling and the roof needs to be ventilated or sealed up tight. However, if sealed up tight most locations do not allow fiberglass insulation against the roof deck.

Any current ventilation, other than that old stack?

Bud

 

[dcobbett]

Hi Bud9051. Yup, you guessed it, I'm in southern California. I'm definitely stretching the definition of "winter" here, but we do get some rain and foggy days here (I'm about 2 miles from the coast).

There is no ventilation, so this would be the 'sealed up tight' type. Originally there was no insulation either, but I had that added (fiberglass type) when I did a renovation about 5 years ago. At the time I didn't know anything about venting vs tight seal vs insulation types, ergo I also have recessed cans up there, which I've heard is a bad idea with a roof like mine.

Having said that, I haven't had any issues with it, and I like having insulation in there because it keeps the temp more regulated in here. Getting away from the original question a bit, but is there a better type of insulation to use in this situation? I was planning on putting the fiberglass stuff back in after the electrician does his thing and I get the roof vent squared away.

Speaking of the roof vent. With this new information, any thoughts?

Thanks!

Dan

 

[PatChap]

Fiberglass is fine, if you don't want it touching the roof deck put in the cheap baffles and leave the 1" air space they create.
If the vent doesnt leak, I wouldn't mess with it.

 

[Bud9051]

The key term is dew point and I can't see as you are at a high risk, plus it has been that way for some time with no issues, although the related issues, deterioration of the wood, my not be apparent for many years.

I stole this line from another discussion forum, can't provide link here and changed the wording slightly, but this comes from one of the top pros.
Fiberglass insulation should not be used on the underside of an unvented flat roof.

My best guess would be to pay careful attention to air sealing, like those can lights you mentioned. Air leaks move a lot of moisture. Beyond that you should be fine.

For a better insulation, read up on Roxul, a high density mineral wool.

Bud

http://ec.tynt.com/b/rf?id=clL5oInf8r5l21acwqm_6r&u=GreenBuildingAdvisor
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[dcobbett]

Thanks for the replies everyone! I think I'm going to just leave the hole, but I'll try to close off the openings with chicken wire or something so I don't get varmints nesting in my nice cushy insulation. I'm looking into using Roxul R23 which would leave an inch or two of space between the insulation and the roof.