Loft insulation thickness re joist height

[AL_z]

Good day,

I am ready to insulate the loft in my 1850-built cottage.The joists in the loft are about 4" (100mm) deep. I may want to partially board out the loft at some point in the future. Should I therefore buy loft insulation that is only 100mm thick? I imagine I could use 150mm thick rockwool, and it would compress down if necessary, but would there be any point?

The other option (in the interest of maximum insulation) is to forget about boarding out the loft, and use 100mm or 150mm rockwool between the joists, then lay large space blankets over the lot. But then, I guess I'd have to kiss goodbye to any ideas of walking around in the loft, e.g., to use it for storing stuff, yes?

The loft is very drafty. Is there an easy way to cut down on drafts coming in between the felt? Or should I not worry about that?

Anyone know if grants are available for loft insulation, and if so, where to apply?

Many thanks,

Al

[george [dicegeorge]]

Draughts in the loft are good, they will remove any water from leaks or condensation so your timbers wont rot and your ceiling wont fall in!

There's been lots of discussion of this in the past, i thinkt hey will advise putting the boards higher with some kind of spacers so you can have thicker insulation.

energy companies have to save energy, they do this by giving away insulation cheap.

[cynic]

Good advice but if you don't want to add to the height of the joists you will still gain dramatically over no insulation by adding 4". You can lay 4" as fill and run another layer crosswise above both base layer and joists. A different higher performance insulation under the boarded area might be a way to go

[Chris J Dixon]

I'm planning to top up my already substantial loft insulation before next winter. The central section is crudely boarded, for storage, and it was suggested to me that, as the simplest solution, I could simply get some seconds of Celotex/ Kingspan, put this on top of the existing boarding, and it would be durable enough on its own.

Is this likely to be so, I've never walked on any. Any particular source recommended for a small quantity of cheap insulation board?

Chris

[NT]

2 good options

1. 4" of insulation, boards, then lay down more insulation

1. add more timber to deepen the joists, rather more work.

NT

[John Rumm]

You would be better laying the insulation over the joists[1] and putting the flooring over that. You can screw the boards down through the insulation so the whole lot stays in place, and the insulation does not compress much.

[1] obviously you can have rockwool or similar in the gaps between the joists.

You can walk on it - but repeated traffic may scuff the foil finish. Also any pint loads would push into it if not protected with a layer of wood over. (even 1/4" ply would be adequate protection in this application)

Where are you in the country?

There is a place near us (SE Essex) that does seconds etc at quite reasonable prices (you could probably do a whole loft in 2" thick boards for a couple of hundred)

[Chris J Dixon]

I already have the original glass fibre between the joists, under the boarding. I was hoping not to have to disturb this.

See my sig.

Chris

[robgraham]

Rather than use more timber make up composite beams from OSB and timber the *width* of your ceiling joists.

I did this recently for a friend. The ceiling timbers were 36mm wide

- the composite beams were 200mm high and the were made so that they slotted over the existing joists. I used 9mm OSB and in this case the

2 joining timbers were 36 x 30. The flooring was then screwed to the top of these beams which made it all very stiff - easy to install, easy on the pocket, easy to make.

I don't think it would be necessary, but you could fill the inside of the beams with rockwool when making them up.

Rob

[george [dicegeorge]]

kingspan/celotex...

or cheaper hardboard, or old carpet.

[g]

[george [dicegeorge]]

sounds good but i dont understand how this saves timber (maybe cos im a bit slow) photo or ascii art please?

[g]

[NT]

I'm guessing Rob means that each old joist has added to it 2x OSB sides, which are fixed together at the top with a strip of 36x30mm timber. Sounds like a lot more work. If you wanted to simplify that one could presumably do that on every odd joist, with the even joists just getting a single sheet of OSB on one side and nothing else.

NT

[george [dicegeorge]]

so the weight of the boarding is held by the screws from the OSB to the original joists?

[NT]

Indeed... that's true of both versions of course. The whole osb idea isnt really a bodge that appeals to me, but it should work. You could add glue fwiw.

NT

[robgraham]

NT - could you explain why you think this is a 'bodge'. Composite beams of this type are frequently used in building construction, as they are light, inexpensive, easy to make, and being a box structure, incredibly stiff. My gut feeling is that you regard the use of OSB as the bodge - OK use ply if you must but the industry is quite happy with OSB for this. ____ II____II II II II II II II II____II II____II IIxxxxII xxxx is existing beam IIxxxxII IIxxxxII

[NT]

If I've understood your diagram right you're using 2 strips of 36x30, I thought you were just using one along the top. It does seem a lot more work than solid timber.

NT

[robgraham]

More work maybe, but how are you going to attach the solid timber ? The bonus I found was the lightness of this beam and the ease of just dropping them over the existing timbers, and screwing through.

More preparation work, but dead easy installation.

Rob

[NT]

right

NT

[Mike Jones]

Could you say which company this is please John? I'm in that area.

Thanks

Mike

[John Rumm]

"APCO Wholesale" is the name I have, but not sure how well they publicise[1] the name as such - but they have a large yard stuffed full of insulation! New and seconds, and a wide range of sizes. Price for

8x4" sheet of foil faced 50mm board is normally about £12 to £14 (depending on if new/second etc). (seconds are pretty decent to be fair). They deliver locally or you can go an pickup. Discounts available for quantity (a LWB hitop van load was about £300 ish last time I ordered).

They are on the A13 in Benfleet, about half way between the bottom of Bread and Cheese hill and Tarpots. Run by a chap called Andy and his wife. Number is 07977 914855.

[1] In fact Google would suggest they do these days ;-) :

[Mike Jones]

Excellent

Thank You.