Insulating Roof

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Mark-J
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Insulating Roof

Postby Mark-J » Wed May 15, 2019 12:41 pm

Hello all :)

I am about to insulate my roof with 100mm thick insulation panels but I am unsure as to which of the three configurations in the attached pic is the best. If it matters, I will be cutting vents into the sides of the fascia and those vents will be level with the gaps between the joists where the insulation panels will be located.

Which of the following three configurations would you suggest I choose?

Thanks all.

Image

JonR
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Re: Insulating Roof

Postby JonR » Wed May 15, 2019 1:10 pm

Is it a tiled roof or flat roof?

Mark-J
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Re: Insulating Roof

Postby Mark-J » Wed May 15, 2019 2:59 pm

Hi Jon,

The roof is flat and is of fibreglass on top of OSB

JonR
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Re: Insulating Roof

Postby JonR » Wed May 15, 2019 6:56 pm

Then push it up tight as under the OSB and you wont need to vent it but insulate and seal it well at perimeters so no air can ingress under the Celotex, version B/C you will get condensation between the deck and insulation so will need venting. Unless you can vent from one side to the other dont do B/C.
Pre warm deck flat roofs we had to cross batten and the put ferrings on top this allowed cross venting over the whole roof.

Thats my take it on it anyways, is this a man cave or extension out of interest ?

Mark-J
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Re: Insulating Roof

Postby Mark-J » Wed May 15, 2019 7:44 pm

It's a 6m x 5m workshop for carpentry and woodworking projects. And yes, I suppose a bit of man cave will inevitably creep into it at some point. I will be spending a good few hours in there almost every day.

So when you say (in your above post):

JonR wrote:Then push it up tight as under the OSB


You are referring to configuration (A)? I've updated the above pic to identify the OSB and Plyboards.

Also, I am thinking of putting vents in the fascia to aid airflow. Here's a pic of what I have in mind, but trouble is, won't I need to place a vent between all joists, and in the front and back of the shed? Is that practical? Can't say I've seen it done on other flat roof sheds but I might be mistaken.

Image

Thanks for the advice Jon, much appreciated.

JonR
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Re: Insulating Roof

Postby JonR » Wed May 15, 2019 10:03 pm

Yes A and no need to vent at all , i would do a mass fill of rock wool myself, cheaper and easier to fit. I would buy a decent brand though of 170mm like Isover or Knauf. You probably should have some kind of back ground ventilation through the shop though say a low level vent at the front and one at the back at high level.


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