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What’s the best way to add insulation to an old outbuilding?
I
have
an
existing
timber
frame
outbuilding
that
I
want
to
convert
into
a
garden
office.
How
do
I
install
insulation
in
the
roof
and
walls
in
a
way
that
prevents
condensation
from
building
up?
The
structure
is
made
of
timber
stud
supports,
plywood
sheets
and
cladding,
with
a
pitched
apex
roof
built
from
OSB
boards
and
EPDM
rubber.
I
believe
if
the
insulation
is
going
on
the
inside
of
the
roof
structure,
that
this
is
referred
to
as
a
cold
roof.
My
understanding
is
that
I
need
to
leave
an
air
gap
of
approximately
50mm,
which
needs
to
be
vented
to
allow
a
throughflow
of
air
to
avoid
condensation.
What’s
the
correct
way
to
achieve
this,
and
do
the
walls
also
need
venting
to
allow
air
to
pass
through
and
escape?
There
is
no
breathable
membrane
installed
on
the
outside
walls,
and
I
intend
to
install
a
vapor
barrier
on
the
inside.
Where all the insulation is below the roof members (the rafters) then, yes, the rafters are on the cold side, so this is indeed known as a cold roof. Normally the roof is vented at the eaves, and you need to allow ventilation at the ridge board to allow air to pass from one side to the other without compromising the structural integrity of the ridge board. In terms of the walls, a breather membrane is typically installed on the outer face of plywood on the outside of the studs. If you don’t have plywood on the outside and this is only on the inside, then that’s a different matter. Timber frame construction, working from inside to out, normally goes internal skin, frame (with or without insulation between the studs), ply, membrane, 25mm spacer batten, cladding – meaning there is a 25mm gap between the plywood/membrane and the cladding.