Introduction: TRULY Insulate Your Loft (or Attic!) - and Save the Planet

Being time rich and money poor, I wanted to cut my outgoings, and be a bit greener.

So I fixed SF40 SuperFOIL to the underside of my rafters to keep warm, cut bills and save the planet:

I chose SF40 because:

a) It nails to the roof, so you can still use the loft for storage
b) It has a radiant heat barrier
c) It is the equivalent of fitting 450mm (18 inches) depth of fibreglass*
d) It should keep us cool in summer too

I expect there are other products you could use, but this one seemed right for us.

There are a lot of steps to this instructable, but it's not as complex as all that. I waste a lot of time talking about nailguns and such. You can skip to step 16 if you want.

NB: Apparently what we Brits call a loft is what our Yankee cousins call an attic. For them this 'ible is about attics.

* Clarification: fibreglass does not block radiant heat; the quilt does. In order to get the same savings, you would have to install 18" of fibreglass. But this does NOT mean that the R values are the same. See the manufacturer's brochure illustrated in the second pic of step 3.

Step 1: And Here It Is

I need the floor space because I keep a load of old tut in my loft. If you don't store things in your loft, you could just lay loads of layers of fibreglass - but you still wouldn't have the radiant heat barrier the quilt gives you and the fibreglass will still have gaps.

You can use insulating boards; but they don't give the same insulation value, and you can't cut them with a pair of scissors.

Step 2: Roof First Please

It's pointless doing any other insulation to your house until you have thoroughly done the roof. The roof is where the major losses are, and heat will seek out the weakest area.

Oh, by all means have double-glazing installed, and fit draught proofing strip. But it won't REALLY make any difference until the roof is done. The current recommended depth for mineral wool insulation is 270mm (, and the more the better, really.

As you can see, I've gone for 450mm equivalent SF40 quilt. Plus we already had 120mm of fibreglass on the loft floor and T&G floor panels on top. We should be toasty!

Step 3: Seal It!

The roof is only as well-insulated as its weakest point. If there's a gap in your insulation, heat will make a beeline for it and escape. It's like pressurising a balloon: if there's a tiny pinprick hole, all the air will eventually escape from it.

So the details are crucial. With a quilted loft, the idea is to make an airtight seal. So don't leave any gaps, or you've wasted your money.

NB - The maker's instructions assume you are going to put a ceiling in to make a liveable space; I wasn't doing this, so used no battens etc.

Step 4: Preparation 1 - TV Reception

This is an internal loft TV aerial.

Have you got one like this?

If you have, don't do what I did, and wait till you have half-installed the quilt, only to discover that:


- you'll need an outside aerial or a dish.

DUH. What a divvie I was.

Step 5: Preparation 1a - Floorboards

I boarded out the loft before I started the job. This has advantages and disadvantages.

The good bit is that you really need those boards to walk on, lie on, kneel on (ouch - my knees) and so forth, especially when you're working in the eaves. You really don't want to put a foot through the ceiling.

On the other hand, it does slightly limit your options when it comes to end walls and eaves.

At the eaves, I'd have liked to staple to the wallplate - but actually that would have been difficult anyway.

Ideally on the end walls I'd have liked to staple the quilt to the last rafter and THEN screw down the floorboards. Instead I made do with stapling to the boards which I had already screwed to the last rafter. I don't suppose it will make much difference.

So on balance, I'm glad I boarded the loft first.

Step 6: Preparation 2 - Choose Your Weapons


'Do you want a staple through your finger? '

It could put an end to your DIY career for ever. So save yourself that trip to casualty, and read this first.

A nailgun is essential - nailing upwards is a pain, and you need to nail every couple of inches to spread the strain and get a good seal. That's a lorra lorra nails.

First, I hired a Paslode gas-powered nailgun with 25mm (1 inch) staples - and that was just barely adequate for the SF40. A standard DIY shop nailgun uses maximum 14mm staples: that will not do the job - or anything like.

But nailguns are scary. If you're not scared, you don't understand the full extent of their power... See step 9.

Step 7: How to Prime the Gas for a Gas-powered Gun

Just in case you have the same issues as me, the gas canister has to be prepared to go in the gun.

It starts out with the black cap sitting a few millimetres proud of the canister - first pic. You need to press the black part hard down against the canister till it drops into a lower position, flat down on the canister - second pic.

It took us hours to work this out from the gun's dismal instructions.

Oh - and be aware that a gas gun pumps out carbon monoxide. This is not good for you. Make sure your space is well ventilated.

Step 8: Preparation 2a - Erm... Not This One

It was suggested to me that a hand-powered stapler of the sort you buy from a stationery store would do - or even a hammer and nails.

Do not even think of it. There will be times when you need to staple through two - and sometimes three - layers of fabric. A hand-powered nailgun will give you RSI in seconds.

But you will want the hammer and nails to tidy up any corners.

Step 9: Preparation 2b - Yes, THIS One

Eventually I bought myself a Tacwise 191EL which fires 30mm staples - albeit only 7mm wide as opposed to the Paslode's 12mm. I found that this was just as good as the gas-powered gun - and in some ways better, as it is lighter to use and needs no gas. And it was only fifty quid.

Keep your hands away from the end of the nailgun. I mean really away. The staples don't come out where it looks as though they might. It really is a gun, and those staples come out ******* quick. I came as close as I ever want to to getting a staple through the finger: the passage of the staple burnt my finger as it passed - that's how close. And I was being careful. So you be doubly careful.

Step 10: Preparation 3

Order your quilt.

The SF40 is twice the weight, twice the thickness and twice as unmanageable as the SF19; but it is equivalent to 450mm of fibreglass (as opposed to 275mm), and for three rolls I paid only 60 quid more. When I bought it, the SF40 was about 140 quid a roll.

I asked the advice of the supplier about how many rolls I would need. He said three. In actual fact I needed five (but I was being extra thorough).

So make your own measurements - like I didn't. :-(

A roll is 1.5m wide, but you will need to overlap it top and bottom, so effectively it only covers 1.2 or 1.3 metres. A roll is 10 metres long.

It is better to over-order than under-order: if you find yourself needing an extra roll of quilt at the last minute - as I did - it will be more costly than buying a load all at once.

Step 11: First Steps 1

OK - now let's start fitting the quilt.

Here are some general guidelines. These are things I learned by screwing up. So you don't need to.

The quilt is light - but not THAT light! The manufacturers say that a roll of SF40 weighs 15kg. You need to hold it up to the rafters, stretch it tight diagonally from previous fixings, and then attach it.

Nailguns are heavy (the Paslode weighs 5kg!). Hold two bags of sugar above your head with one hand, stretch a piece of fabric above your head with the other hand, and then press a trigger. You will be tired. You will be hot. You will sweat. TIRED HOT SWEATY PEOPLE HAVE ACCIDENTS.

So work in short bursts. When the sweat runs down your face will be a good time to stop. Our first length took two of us three hours to fit - because the first is most difficult, and we were getting the hang of it. (Yes - pun intentional. Sorry.)

Step 12: First Steps 2 - Timescale

My loft is just shy of 20 feet long. Working alone, I found I could do two lengths in a day. OK, I'm unfit. So maybe you can do three, Mr Macho. But even with two of you on the job, retro fitting a loft is several days' work.

Obviously if you fit the quilt before the roof goes on it's easier. But I didn't plan to reroof the house just yet awhile.

It is a two-person job. I fitted a lot of quilt on my own, but I didn't enjoy it, and I made a poor job compared to when I had a mate.

Also, some of the work is uncomfortable and unpleasant (eg squeezing into the eaves): it's nice to share it with a friend. Even better with an enemy...

Step 13: First Steps 3 - Plan Your Lengths

The instructions say to fix strips of fabric horizontally. That is what I did in the main roof space - though when it came to the eaves I made some vertical strips, as you'll see later. You can use the quilt vertically throughout if you prefer (along the rafters instead of across them) but you will have to deal with many more joints, which means more wasted fabric and loads more sealing tape.

Make sure you get your overlaps right. I found that the margin between the seam and the edge of the fabric was about right, making an overlap of about 8 inches. The manufacturers say a 3 inch overlap is enough - but I found the slippery quilt slides around a lot, and a 3" overlap soon becomes an 'oh, whoops, it doesn't quite reach'.

Make sure all joints of fabric are where you can get at them. I didn't.

Try not to make cuts longer than they have to be. A cut more than a foot or so is only going to waste fabric: you're better off making a slightly larger overlap at the other side.

Consider using short lengths: they are more manageable. On the other hand, joints are tiresome and waste fabric.

Start nailing from the top: let gravity stretch the fabric for you. Otherwise you're pulling against it. You will want to keep the fabric taut in two directions in any case - three is impossible.

Step 14: First Steps 4 - Right to the Eaves

It is crucial to take the fabric right into the eaves - but also essential not to block the gap between roof and rafters. The design of my roof makes this difficult; I made a series of trays and stitched SF40 onto them. The upright parts of the trays keep the gap open for air movement, while the base holds the quilt down to the wallplate.

I'm not sure this is the best solution. It certainly used up a lot of fabric, and means a lot of joints to tape over in a confined space.. But I wasn't comfortable just nailing the quilt to the floorboards.

Step 15: First Steps 4 - Tips and Tricks

When you get the hang of it, you can use the nailgun nose to press the fabric against the rafters and fire in one action.

Initially fix the quilt strips with a hammer and a few nails - just enough to get it in position. Then you can easily adjust if you need to.

Do not stint on light. You need to see what you are doing. Hire or buy a halogen lamp if you need to. The alternative may be a 25mm staple through your finger: which would you prefer?


Keep your hands away from the end of the nailgun. I mean really away. The staples don't come out where it looks as though they might. It really is a gun, and those staples come out ****** quick. I came as close as I ever want to to getting a staple through the finger: the passage of the staple burnt my finger as it passed - that's how close. And I was being careful. So you be doubly careful.

Step 16: OK - Off We Go: First Length of Quilt

OK. So cut a length of quilt the same length as your loft. (Actually, a tad longer would be wise.)

TIP: You'll find it easier to cut the quilt DOWNSTAIRS, and carry the cut length up into the loft.

Start in the middle of the roof, at the highest point. Staple your length to the rafters.

If you have nasty trusses getting in the way (like I did) you'll need to cut slots in the fabric so you can pass the fabric around the uprights.

Try not to make cuts longer than they have to be. A cut longer than a foot or so is only going to waste fabric: you're better off making a slightly larger overlap at the other side.

Make sure all joints of fabric are where you can see them - otherwise a beam is going to get in the way of the joint, making it more difficult to staple to the rafter AND to seal with tape afterwards.

Just like I didn't...

Step 17: Second Length

Overlap the second length of quilt over the first, and tack to the rafters.

Step 18: More Lengths

Keep cutting and fitting more lengths in the same way.

Step 19: Cut Around Obstacles

Make cuts in the fabric with a long pair of scissors so you can go around upright members or any other obstacles.

Step 20: Gradually Tack Around It

Then gradually tack the quilt up to the rafters all around the obstacle.

Step 21: Cut Round More Obstacles

Cut the quilt to fit around any pipes or protrusions.

Be really careful to get a good seal here: it's a weak point in the process.

Step 22: Keep Adding Lengths Till You Get to the Eaves

Now you need to decide how you are going to handle the eaves.

The instructions tell you to fasten the quilt to the wallplate. The design of my roof made this virtually impossible. Instead I made little trays, nailed the quilt to them, and slid them into the eaves.

You'll have to adapt to the conditions in your loft. Just make sure:

i) that the insulation goes right over the outside wall

ii) that you leave an airspace between the roof felt and the quilt - otherwise you'll get condensation

Step 23: Keep Going Till You've Covered the Whole Roof

Here's a pic supplied by the manufacturers. Mmm - how lovely. The lucky owner of this roof space hasn't got single joint to make.

I hope your loft is the same. Mine wasn't. Grrrrr.

I had loads of tricksy truss members to work round.

Never mind: start at one end and keep going till you get to the other. There's no rush. After all, you've got until next winter....

Step 24: Now Cover Any End Walls

I used a thinner and less expensive quilt for these, as I live in a town house and I just wanted to stop my neighbours benefiting from my heat...

If your gables are external, it probably makes sense to carry on with the same quilt you've used for the rest of the roof.

Step 25: Joints Between Roof and Walls

Seal 'em up as usual with foil tape.

Remember - we're trying to make our loft into one huge airtight plastic bag.

Step 26: Tidy Up Any Trailing Ends

Tape up all these overlaps with a good slug of tape.

Step 27: Now Tape Over All the Joints

Use plenty. We are trying to create an airtight envelope.

If you find big gaps, cover them over with a small piece of quilt and tape over.

(Oh yes. Tape over all the joints, he says. How easy that sounds. In fact it's a bit like Shaeffer's famous stage instruction in The Royal Hunt of The Sun: They cross the Andes. Easy to say...)

Step 28: And You're Done

I shan't know the full effect until next winter. But we felt an immediate benefit; the house was warmer and cooled down much more slowly from the warmth of the day, reducing the need for heating.

I was able to turn off the central heating in mid-April - whereas in the past, it's been on well into May (though that could just be the nice spring we've had).

The other thing I did was go mad on draught-proofing, surrounding all the external doors with door seals, putting a rubber weather seal under the door of the integral garage and so forth. Well worth the money and time.

Step 29: Wait for It to Snow

Yes - you DO want it to snow.

Because then you can go outside and look at all your neighbours' roofs (rooves if you prefer) and see the snow melting on them. While on yours the snow stays there unmelted.

This is a sure sign that no heat is escaping from your roof. Hooray!

One planet saved.

Now - how about a rainwater capture system?

Stay warm!

Step 30: Footnote on R Values and Radiant Barriers

These pics are from the two data sheets on SF19 and SF40 quilt. The crucial point is to distinguish between Conventional R Value  and Comparative Energy Saving Equivalent R Value. As you can see, Conventional R Values do not make allowance for the radiant barrier.

So any question of doubling depth and doubling R value is not relevant. The question - if there is one - is whether increasing the depth of the quilt increases the Comparative Energy Saving Equivalent R Value, and the two data sheets explain the difference between SF19 (19 layers) and SF40 (36 layers).

Essentially, the latter is 50% more effective than the former. Hope this helps.

Note that as explained in earlier steps, I have added quilt to an existing 120mm layer of fibreglass. So I now have 120mm fibreglass (R= about 6), a layer of chipboard (R= about 1), and the SF40 (R= about 2).

But taking into account its radiant properties, the SF40 has an equivalent R value of 9.6.

For more explanation see (especially 4.3: The limitations of R-values in evaluating radiant barriers).

Also for a chart of R values of various materials.