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.

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.

can you see any writing?

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

Purpose made for retro fits

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.

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

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

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 £5). You will need a 60mm tank cutter (set from B&Q £5) to bore the holes in the soffit. Be careful to avoid the ends of the roof joists in the soffit /facia box.
Frank

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

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.

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.

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.