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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. |