Reasons not to put Insulation ( Anticon ) in the eaves for a flat roof house?

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Reasons not to put Insulation ( Anticon ) in the eaves for a flat roof house?

(5 posts) (5 voices)

Started 1 year ago by peterx
Latest reply from Andy Mcleod

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peterx
Member

Insulation in the eaves for a flat roof house
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I have a flat roof house.

I have a installer telling me it is not standard practice to put insulation (batts and/or anticon) in eaves of a flat roof house. ( Anticon is a tradename for glass wool insulation that is attached to a roll of alumimiun foil )

Bats are placed resting on the ceiling.
Anticon is directly underneath the roof metal sheeting, with the metal foil facing down.

I can understand not putting bats in the eaves of a flat roof house.

I asked for anticon to be placed over the total roof space - INCLUDING the eaves.
My reason for (asking for anticon be under the roof metal in the eaves ) is to stop heat getting into the roof space ( via the eaves )

THe total roof area is about 110 m2 .
The eaves of the house are about 1 foot wide.
I estimate the eaves total area is about ~10m2 or near 10% of the total roof area.

THe eaves are ventilated with groups of narrow slots .
Each group is about a 1m apart.
A group consists of about 3 slots close together.
Each slot is about 200mm long and 5 mm wide.

Are there valid reasons for not placing anticon under the roofing iron that is above the eaves ?????????

The only thing I can think of is that it may be to do with moisture condensation?

I do not trust the answer from the installers , which is " thats what we always do ".

Thanks in advance

Posted Thursday 11 Mar 2010 @ 3:34:01 am from IP #
Daniel Boon
Member

There is no need to instal insulation in the eaves area; insulation should go from the top plate of the surrounding walls inwards an totally cover the entire roof / ceiling area. Cellulose is the ideal insulation for several reasons.
53% of the Sun's solar spectrum is infrared heat, once this ray hits a steel / tile roof, the wave length of the radiation changes and the heat is progressively store and radiated through the roof material and then through the insulation foil and even fibreglass (which starts breaking down from the day its installed).

Moisture that enters via vents in the eaves then is stored on the fibreglass strands and - as you probably already know - air is the best insulation (0.3R is the average accredited addition to a 3.2R batt to achieve 3.5R); however, air laden with mositure actually helps transfer heat ...

How thick is the foil / fibreglass batt ? Have you considered cellulose (its more effectively 'installed than attempting to affix foil - with no gaps - on roof trusses.

Email me on danielboonjp@gmail.com for a rely as I don't frequent the site often.

Posted Thursday 11 Mar 2010 @ 6:16:24 am from IP #
dymonite69
Member

The major heat load comes from the radiant heat load from the sun. Foil addresses that adequately. Any remaining heat entering the roof space air has insignificant effect on heat penetrating through the ceiling into the rooms below. However, foil over the eaves may reduce the eaves radiating heat onto the walls and windows.

Posted Thursday 11 Mar 2010 @ 10:33:05 am from IP #
gully
Member

In my mind batts are for winter insulation, reflective stuff (sarking etc) is for summer insulation - anti-con is kind of for both as well as sound-deadening for tin roofs.

Problem with some buildings are the eaves aren't air-tight at all and like you say, air will enter via the eaves and create a draught. If you have whirlybirds on a pitched roof this can be a good thing (chimney effect), but on your roof it's all at one level.

You could put insulation in the eaves to stop the draughting (to some extent), but
i'd suggest it better getting one of those solar roof fans if you can, to exhaust the hot air and use convection to cool the roof space (the chimney effect).

http://www.belledaylighting.com.au/content/show/20003

Benefit of this solution is, if there's no sun, the fan won't run eg. overcast/rainy days, unlike whirlybirds.

Posted Wednesday 17 Mar 2010 @ 1:39:13 am from IP #
Andy Mcleod
Member

There's good reason to insulate your eaves, depending on what you line your eaves with.... some cement sheet manufacturers require a flat roof above lining to be insulated to avoid thermal stresses. Also, despite the compression of insulation over graded battens ( or skillion?)you'd still get a differentiation in roof planes if you don't change the thickness of your battens where its uninsualted...I love flat roofs with wide external eaves, we use a 1 degree pitch where ever we can, so variation in the underlay would create installation problems, we also place a blanket under the entire roof, bulk insulate between rafters (that depends a lot on the type of your roof structure) and tape our wall insulation to the roof blanket to create a continuous seal.
PS Sorry this is late, saw the post and we've been dealing with this issue so...

Posted Tuesday 18 May 2010 @ 11:38:57 am from IP #

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