"Andy Hall" wrote in message
...
On 17 Feb 2004 01:50:42 -0800, (Andrew)
wrote:
Andy Hall wrote in message
. ..
I insulated my single brick garage using Celotex by first making stud
framing in 75x50mm timber. The rectangular sections produced were
bolted to the floor using Rawlbolts and to the joists using carriage
screws. The rear face of the timber was spaced off from the wall by
about 25mm. The Celotex was cut and friction fitted into the frames
and then the joints taped with foil tape that they supply. Finally,
I clad the framing with 18mm ply. Having the timber framing spaced
off from the wall prevents cold bridging from the wall (although it
does allow some with the floor).
Rigid foam insulation could have been between the floor and the wood
framing. Rawlbolts can go through the foam and into the wood. A nut and
washer on a rawlbolt thread either side of the framing sole plate will
support the timber.
An alternative would have been to
bolt the timbers directly to the wall but this would have bridged the
insulation - not necessarily that big a deal in a shed, although you
wouldn't do it in a dwelling. The cladding means that I can fit
light to medium weight things anywere on the walls with no hassle and
for heavier things I have very substantial studs at 600mm intervals.
I want to do something similar and had wondered why you used the
framing method (found in the archive). Now I understand.
Do I need ventilation for the airgap behind the celotex?
It's probably a good idea. As a general principle, putting wood in a
potentially damp and unventilated space is not a good plan. Because
of the construction of my garage, I was able to incorporate
ventilation quite easily. The overhang of the roof provides quite
generous horizontal soffits under the eaves. The roof uses trussed
frames similar to house construction. I fitted Celotex to the
inner surface of the rafters - I could have fitted some between and
some on top, but it was enough of a PITA to fit the stuff up there
anyway that I didn't mind losing about 50mm of depth up there.
This created a space behind the depth of the rafters to ventilate the
them. I then boarded on top of the joists to form a storage area but
only up to the roof Celotex. The wall framing was arranged so that
there was an air gap at the top meeting the gap behind the roof
Celotex. I then fitted soffit vents into the soffits between each
pair of rafters on both sides of the (apex) roof.
This gives a ventilated space common behind roof and walls.
I did a simple test using smoke matches held against holes cut in the
final wall on a mildly windy day. It was blown in and out, so I
think that the ventilation is effective enough.
An alternative would be to chop an air brick into the wall, I suppose.
For belt and braces, I used pressure treated timber for the framing as
well. A good and cheap source of this is a timber mill that makes
fencing materials, although it can be obtained at a normal merchant.
Is there another airgap between the celotex and the plywood or do you
fit the celotex flush with the outer face of the battens?
No. The Celotex is fitted flush with the front surface of the
framing. I then taped it using the metalised tape, to cover the
joins from sheet to sheet and to the battens. In a few places where
there were small holes and gaps as a result of the garage
construction, I used foam filler.
I then fitted the ply to the framing using drywall screws and painted
it.
The celotex app notes also suggests using it to insulate the floor
with a covering of flooring grade chipboard. Anyone done this?
I debated the idea. The problem for me is that the height from
floor to joists is only about 2400mm and I didn't want to lose any of
that. Also, I will want to move heavy things in and out on occasions
so I don't really want a step at the front.
I had done the heat loss calculations for the building and the floor
was the least of the losses. Now of course it's the most, but not
substantial.
Andrew
.andy
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