Ever wondered what £999 (this included VAT and delivery) worth of Black Mountain Sheep's Wool Insulation looks like? It arrives on two pallets (which can easily be moved by one person). Each pallet had 18 rolls. The total of 36 rolls covers around 55 squared meters. The pallets always come in handy for building that compost heap you always promised yourself you would build if only you had a few old pallets! It took a couple of days to haul this lot into the attic. It isn't heavy just bulky and very dirty. The rolls are mostly well wrapped in plastic bags but not all. Everything is covered in a layer of black dust that will settle around your house whilst you move it. I can only assume that the place this is made in Wales is co-located with an old coal pit. The alternative to Black Mountain is Thermafleece but that is 30% more expensive. Why did we choose sheep's wool? Well it has vastly lower embodied energy than mineral wool but the aspect that really swung it is that it can be handled without gloves and causes no skin irritation. Thus it can be used over top of the existing mineral wool to 'seal it in'. This should make the loft a much nicer environment to move around in. Anyone who has ever spent any time in a loft insulated with exposed mineral wool will tell you that it gets in your lungs and makes for an uncomfortable experience.
The picture (right) shows the next stage of operations in the attic. Each one of the seven recessed ceiling lights need to be sealed into airtight boxes. Each box had to be made up from materials to hand. I bought some 47mm x 47mm batten as the existing joists are 94mm deep. A couple of these, cut to length, slot into the gap between the joists. Screw in good 75mm (size 8) screws through the joists and into the ends of the battens, Then a third, longer, length goes over top of the joist so that the unit is load bearing. Put two of these either side of the light fitting and smaller lengths along the joists to make the remaining sides of the box. The battens can be screwed or glued but make the unit robust enough to take being stood on. Then cut a section of chip board (or whatever you have to hand) to fit over top as a lid. I used self-adhesive door seals (visible in the photo) between lid and box to get a good seal. You will have to include some holes to allow wires in and out but you can mastic all round for a good seal.
You can screw the lid down but there shouldn't be a need to be too thorough. Remember that you may need to get to the top of the light again, one day, for maintenance. This will effect whatever you put over top of the air-proof box too so think about it! Next step is to lay the first insulation. At this point everything should be easy for most DIYers. You have to remember to lay any electrical wiring over top of the insulation in case it generates heat. This will also ease maintenance. Whoever laid the wires in our loft took no notice of this advice so we had to dig around to find all the wires. Several wires were threaded underneath walking planks near the base of the inverted A-Frame. In theory you could unwire these and do the job properly but we didn't worry. We made the next phase difficult for ourselves as we wanted to be able to walk over the insulation in places and have some storage. The normal advice is that extra loft insulation makes storage impractical. Other advice tells you it can be done but to more than 40% of the attic should be boarded. My enquiries lead to no good explanation or advice on the matter.
Therefore we had to use common sense. If your attic is to be lived-in, rather than used for storage, then Building Regulations require proper load-bearing joists to be installed. Apart from that we guess the only limits are the extra weight you add to the attic joists if 'over-joisting'. Hence, restricting the amount of over-joisting, to save weight, seems a good idea. We planned to fit the 40% and bought enough 100mm x 47mm joisting as seemed sensible. It will be spread evenly through the attic space and must be screwed to the existing joists using "L" angle-brackets. The insulation is 100m thick and we will be making two passes to get the additional 200mm. The first layer will go at right-angles to the existing joisting then the second layer at 90 degrees again. Hence the two layers of over-joisting will be angled to match. This provides a strong but lightweight frame. Remember that all this weight is in the attic so, even if you screwed everything down firmly, to make the loft floor stiffer, the house underneath has to hold it all up! Therefore we preferred a minimalist structure with no attempt to make the existing ceiling stronger.
Try and position the load around the sides of the loft, near the load-bearing walls, rather than the middle. Do not add over-joisting over existing pipe-work or obscure access to the stop-cock valves. (You may need those in a real hurry one day!) If you (like us) are planning for future installations of Solar Thermal or Photovoltaic Panels then think about where additional pipe-work or wiring will go. Provide routes around or through any raised flooring so that work can be done without having to rip out all your good work. This may all seem like hard work. And it is. However, if you call someone in to do some work in the attic, a few years down the line, then it will all be worth it as your installers will be able to move around and work without putting a foot through your ceiling. Just make sure that the new flooring doesn't get in their way. So keep it to a minimum. The roof joists are already holding up all your water tanks so they are quite strong. They also sit upon a rigid box structure so will take a reasonable static load. If in doubt get a builder in and talk to your Local Building Control Officer.
Over-boarding (as illustrated) is necessary for any areas where you may need to access. Follow the advice on the pack and do not allow it to be supported by joists further than 600mm apart. Do as we have done here and mark the position of all wiring, pipes and ceiling lights on the top of the boards for future reference. You are not meant to trap the wires between boards and joists although this is probably more to do with stopping you from drilling through them. We cut slots in the over-joists to fit the wires through. (Do not cut such slots into your ceiling's load bearing joists!) As long as some air can pass then over-heating should not be a problem. We also avoided having to thread wires over joists as much as possible by routing them around the joists however, sometimes, the available lengths did not allow this. In areas where access is not likely to be required you can probably get away with spare furniture board, and the like, whatever you have lying around. However this stuff is dangerous if you try and step on it as it is unsecured. This kind of thing is only good for static storage.
Update March 2010: when we used Black Mountain Sheeps Wool we found that some of the rolls didn't fluff up to the full 100mm advertised. As we had plenty to spare we didn't worry about it and just laid a third layer where necessary. The problem mostly effected the centre of each roll where the wool was most compressed. We spoke direct to Black Mountain about this when we visited their stand at Ecobuild 2010 in Earls Court, London. Although they said they knew of two other clients who had reported the same problem the wool normally self-inflates to the full width after a few days. They do sample-check the product and had detected no problems. If this is to be believed it seems we were unlucky on this occasion. To their credit they were were very gracious and offered to give us free rolls! We declined this offer as unecessary and wished them luck. Caution is still advised. If it doesn't rise to the full width after a few days give the manufacturer a call as they seem interested in rectifying the problem and are happy to help.