Green Building Forum - Insulation

Insulation

cha0s — Wed, 16 Dec 2009 22:15:52 +0000

This has probably been asked a million times on a million forums.. but.. i couldnt find a decent answer. so..

Im going to add insulation to our loft.
How much air gap should I leave round the eaves.
How do i tell if i have breathable felt/whatever.
If i have the breathable stuff do i need an airgap?
If i need an airgap, is there some nifty (and cheap) plastic moulding i can use to maintain the gap?
And.. in one room we have sloping (slopeing?) ceilings on one side.. can i shove rock wool insulation down there, as the current pink foam boards dont seem to be doing much.

Also, i have it in my head that i need to insulate over the cavity, so cold air dosent get down there, I think there is cavity insulation (rock wool batons ??) but i bet cold air will still get between the insulation and the wall!
So do i need to do this?

Thanks.

Insulation

jamesingram — Wed, 16 Dec 2009 22:36:55 +0000

he's a go

1 .25mm
2. is it thick and stiff , tar ry, then its old style non breathable
3. yes
4. yes ( probably still a good idea)
5. not if you fill the air gap
6. yes

Insulation

tony — Wed, 16 Dec 2009 22:37:48 +0000

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4191&page=3#Item_1

try that thread re cavity batts.

25mm gap over insulation at eaves,, anything will do -- egg boxes, old gutter etc 50mm over sloping soffits ( you can use search to read about these or skeiling ceilings ) thermal bypass is what you have there now -- insulation doing nothing.

most likely not breathable felt if black or brown then not for sure, good idea to insulate the cavity and to join it up to the loft insulation.

Insulation

cha0s — Thu, 17 Dec 2009 08:15:07 +0000

great thanks.

I think the felt has a white backing. and is more of a fabric than the usual tarry stuff.

Insulation

tony — Thu, 17 Dec 2009 08:50:11 +0000

can you see any writing?

Insulation

cha0s — Thu, 17 Dec 2009 10:40:25 +0000

hmm.. cant remember.. ill have a look at the weekend when im up there.

Insulation

sinnerboy — Fri, 18 Dec 2009 00:26:17 +0000

http://www.vents.co.uk/pdf/rv600.pdf

Purpose made for retro fits

Insulation

cha0s — Fri, 18 Dec 2009 09:55:16 +0000

that looks like just the thing.

any idea of cost?

Insulation

tony — Fri, 18 Dec 2009 11:31:32 +0000

they are easy to use on new build so long as they get built in with the roof but not at all easy to retro fit -- they are very similar to egg boxes. -- for retro fit remove flat bti at the bottom.

Insulation

sinnerboy — Fri, 18 Dec 2009 13:40:37 +0000

Carefull here - it is most important that air does not flow through the fabric of the insulation quilt thus convecting away its thermal performance dramatically . That product must be installed in "upside-down-7" format to acheive this ( ie admit vital ventilation flow to attic void but not through insulation fabric ) -despite the hassle factor . Sorry cahOs don't know Â£ cost

http://www.richmondbp.ie/downloads/pdf/roofvent_gvb_full.pdf

the RV635 and 655 on page 22 of the above is an alternative - would you mind posting the Â£ comparison f you discover ?

Insulation

jamesingram — Fri, 18 Dec 2009 13:56:47 +0000

what about the rv200 ?
or Continuous Rafter Tray (Rollout)
http://www.fascias.com/en-gb/dept_745.html

Insulation

sinnerboy — Fri, 18 Dec 2009 14:32:39 +0000

Not practical for DIY retro fit - you need to remove tiling felt and battens and fix from over roof . Many of the details in the Glidevale brochure fail to address the issue of wind penetration of the insulation .

http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18751,en.pdf

Look at "General Notes" to details 1.09-1.15 in the above document

Insulation

jamesingram — Fri, 18 Dec 2009 15:00:55 +0000

I've cut them down and just stuffed them in between the rafters to create the gap between insulation and felt , seemed ok

Insulation

sinnerboy — Fri, 18 Dec 2009 15:35:51 +0000

Well yes - that will provide ventilation to the attic void - but will not prevent wind penetration through the leading edge of the insulation

Insulation

chuckey — Fri, 18 Dec 2009 16:09:07 +0000

Without a sketch of you actual arrangement its a bit difficult, here goes anyway:-
1. Cut up your G/F into strip say 1m long, roll up and stuff into top of cavity as tight as you like. When you get your blown in cavity insulation the workers will like this, but in the mean time you are turning the gale up your cavity into a trickle.
2. Gather some plastic bags, or some other plastic film , cut it into bits say 24" wide and again 1m long (for handling) and run it along the base of your roof with its bottom end overlapping your new cavity stuffing a little or even pushing it down so its caught between the stuffing and the OUTSIDE brickwork. Go around and temporarily tape the top edge up to the underside of the roof. Now slam in as much glass G/F as you can afford. When this is done, drop the plastic sheets down over the G/F and push bits of 2" X 1" on edge every 12" of so, so the draught can flow OVER the edge of the G/F.
If you are unsure of you eave ventilation, put in plastic 60mm round vents every 4' (bag of 5 for Â£5). You will need a 60mm tank cutter (set from B&Q Â£5) to bore the holes in the soffit. Be careful to avoid the ends of the roof joists in the soffit /facia box.
Frank

Insulation

EasyBuilder — Fri, 18 Dec 2009 21:38:43 +0000

How about using these (http://easyvent.com/) and filling the limited space at the eaves with insulation? I'm confident that it would be effective in removing condensastion, but would it satisfy the regs?

Insulation

sinnerboy — Sat, 19 Dec 2009 01:38:48 +0000

The "belly up" part of that product would foul the drainage gulley of the draped sarking felt . I would not use it

Nor would i wrap loft quilt in polythene - and thereby contravene Part B (B2) of of the building regs (Fire ) - the attic floor should not be lined with such flammable materials

Insulation

jamesingram — Sat, 19 Dec 2009 10:06:55 +0000

I've used off cuts of PUR board ( Kingspan, celotex etc)wegded inbetween the rafters say =<50mm thick to create the 25mm vent gap , then stuff fibre insultion up tight to this ,
tricky to retrofit , especially past the wall plate and over the cavity, but do-able in some situations , easy to do from the outside , if you lift the fisrt few rows of tile or happen to be reroofing
good way to use up off cuts as well
though I've used them ,those roll out rafter vent I mentioned seem way over priced for what they are

Insulation

tony — Sat, 19 Dec 2009 10:31:40 +0000

I never use the roll out ventilation stuff, I simply leave a gap when I insulate. But then I do the insulation before the roofing lots easier and so much nicer than working inside a loft.

Insulation

suegreenbuilding — Sun, 03 Jan 2010 14:07:53 +0000

The GreenSpec website is very useful, e.g. see

http://greenspec.co.uk/html/refurb/unvent_roof_insulation.html
http://greenspec.co.uk/html/refurb/vent_roof_insulation.html
http://greenspec.co.uk/html/refurb/loft_insulation.html

Insulation

cha0s — Thu, 07 Jan 2010 12:58:16 +0000

well.. i did the insulation over xmas, happy xmas to me!

all the talk about venting and the like proved to be a waste of time, as there is no eave ventilation.
Well.. there wasnt :-)

Ive installed a load of 70mm round vents in the soffits.
And will be getting the "upside down 7" eave vents at some point.

Most of our felt (or whatever) is breathable i think, but some isnt.. and its quite wet. Hence the new vents.

Another thing is we have solid walls on part of the house (think its 1850's) which i decided to drill holes through to get the ventilation from the eaves into the left space. probably no where near adequate, but better than nothing.. plus it was very cold to be standing around outside.

Insulation

djh — Fri, 08 Jan 2010 12:05:37 +0000

Tony, if you do insulation before roofing does that mean you're dependent on good weather? Or just lots of tarps or something.

Insulation

tony — Tue, 12 Jan 2010 09:31:30 +0000

Never used a tarp -- it did sometimes rain but only once hard -- the water rarely got through the insulation mostly sat on top -- never was a problem -- we nearly always insulated the same day as we felted in -- did it on both flat roofs and pitched -- biggest roof was 300 ^2 and that was double tacked -- generally any water or moisture in or on insulation will get evaporated away within a few days -- may be not so fast in these cold climatic conditions but it will go -- with a vb no harm will result.