I have a 1930s house with the ground floor consisting of wooden floorboards
on timber joists. In turn, the joists are supported by brick pillars or by
the main walls. Under the floor there is a 2 foot high crawl space
ventilated by airbricks. There is access via several crawl hatches. The
underlying soil is dry to the touch.



I'm looking to insulate under the floor without removing the floorboards.



I've read about various possible approaches using rockwool / loft insulation
roll between the joists suspended by net / nylon cord / battens, or
alternatively using rigid panels of Kingspan / Celotex / Floormate cut to
fit between the joists.



Are either of these approaches sensible and practical, or are the any
alternatives? Or alternative products to use?



If I use rigid panels, I have concerns about creating a possible future damp
problem if I block up the end of this cavity/channel and air is effectively
trapped in a cavity between the underside of the floorboard, the joists, and
the rigid panel. If I don't block the ends of this cavity, is it just a
waste of time? Or should I push the rigid panel next to the underside of the
floor board?



Presumably I should not have insulation in contact or close proximity to
electric cables for risk of leaching chemicals from the cable insulation?



What are the possible options and suggestions?

On Sun, 15 Oct 2006 18:02:42 +0100, "JM" wrote:

|I've read about various possible approaches using rockwool / loft insulation
|roll between the joists suspended by net / nylon cord / battens, or
|alternatively using rigid panels of Kingspan / Celotex / Floormate cut to
|fit between the joists.

Beware loose rolls of insulation which will fall on your head and itch
terribly.
There is glass fiber roll on a polythene outer, which should be better.

Polypropylene cord on clout nails will hold it up OK.
--
Dave Fawthrop dave hyphenologist co uk Google Groups is IME the *worst*
method of accessing usenet. GG subscribers would be well advised get a
newsreader, say Agent, and a newsserver, say news.individual.net. These
will allow them: to see only *new* posts, a killfile, and other goodies.

"Dave Fawthrop" wrote in message
...
On Sun, 15 Oct 2006 18:02:42 +0100, "JM" wrote:

|I've read about various possible approaches using rockwool / loft
insulation
|roll between the joists suspended by net / nylon cord / battens, or
|alternatively using rigid panels of Kingspan / Celotex / Floormate cut to
|fit between the joists.

Beware loose rolls of insulation which will fall on your head and itch
terribly.
There is glass fiber roll on a polythene outer, which should be better.

Polypropylene cord on clout nails will hold it up OK.
I insulated with rockwool held up by wire strung zigzag fashion between
nails I hammered into the joists. As mentioned, although this works you will
need long gloves, a boiler suit, goggles, a facemask and a scarf to protect
you from the rockwool as it sheds fibres directly onto you: not nice.

Also, in retrospect I would have used some form of netting to hold the
rockwool in place, not wires, since netting would hold it in place more
positively. The cheapest way to do this IMO would be to use garden netting,
or maybe garden fleece or membrane.

A scan of my floor with an IR thermometer showed ( referenced to a spot I
didn't do because I ran out of rockwool ) a 1 degree Fahrenheit difference,
occasionally 1 degree Centigrade, so a worthwhile result.

I would say that the silvery bagged rockwool I have seen is somewhat more
expensive than the loose roll version so if economics is all, rockwool on a
roll plus netting may be the cheapest option.

Andy.

JM wrote:
I have a 1930s house with the ground floor consisting of wooden
floorboards on timber joists. In turn, the joists are supported by
brick pillars or by the main walls. Under the floor there is a 2 foot
high crawl space ventilated by airbricks. There is access via several
crawl hatches. The underlying soil is dry to the touch.



I'm looking to insulate under the floor without removing the
floorboards.


I've read about various possible approaches using rockwool / loft
insulation roll between the joists suspended by net / nylon cord /
battens, or alternatively using rigid panels of Kingspan / Celotex /
Floormate cut to fit between the joists.



Are either of these approaches sensible and practical, or are the any
alternatives? Or alternative products to use?



If I use rigid panels, I have concerns about creating a possible
future damp problem if I block up the end of this cavity/channel and
air is effectively trapped in a cavity between the underside of the
floorboard, the joists, and the rigid panel. If I don't block the
ends of this cavity, is it just a waste of time? Or should I push the
rigid panel next to the underside of the floor board?



Presumably I should not have insulation in contact or close proximity
to electric cables for risk of leaching chemicals from the cable
insulation?


What are the possible options and suggestions?

Use polystyrene, it's available in various thicknesses, 100mm should be
ample.
it's clean and cheap.
it's easy to work with.
A slight downside is that it gives off toxic fumes if it catches fire, but
when was last time you had a fire under your floor?
Celotex et al will set you back more than you could ever save and
fibreglass/rockwool are horrible for working with.

JM wrote:
I have a 1930s house with the ground floor consisting of wooden floorboards
on timber joists. In turn, the joists are supported by brick pillars or by
the main walls. Under the floor there is a 2 foot high crawl space
ventilated by airbricks. There is access via several crawl hatches. The
underlying soil is dry to the touch.



I'm looking to insulate under the floor without removing the floorboards.



I've read about various possible approaches using rockwool / loft insulation
roll between the joists suspended by net / nylon cord / battens, or
alternatively using rigid panels of Kingspan / Celotex / Floormate cut to
fit between the joists.



Are either of these approaches sensible and practical, or are the any
alternatives? Or alternative products to use?



Both work.

But kingspan/celotex is probably the easiest and most effective, and the
most expensive.


If I use rigid panels, I have concerns about creating a possible future damp
problem if I block up the end of this cavity/channel and air is effectively
trapped in a cavity between the underside of the floorboard, the joists, and
the rigid panel. If I don't block the ends of this cavity, is it just a
waste of time? Or should I push the rigid panel next to the underside of the
floor board?


The latter. Push it up. However thats all on the 'warm' side of the
insulation so it should not be a big problem.




Presumably I should not have insulation in contact or close proximity to
electric cables for risk of leaching chemicals from the cable insulation?


Not an issue with celotex. Its very inert


What are the possible options and suggestions?

If I use rigid panels, I have concerns about creating a possible future
damp problem if I block up the end of this cavity/channel and air is
effectively trapped in a cavity between the underside of the floorboard,
the joists, and the rigid panel.

It should be fine. To avoid condensation, each void should be considered
either part of the outside (i.e. outside the insulation envelope and well
ventilated) or part of the inside (i.e. inside the insulation envelope and
with at least some ventilation to the rest of the house).

You want to avoid void areas sandwiched with insulation both towards the
outside and inside, as you can get interstitial condensation unless the
insulation is "short circuited" with ventilation.

The space between the rigid insulation board and the floorboards should
count as part of the inside.

Some ventilation to the cavity would be good particular if you have an
impermeable floor covering. However, it should be ventilated to the house
space, not the underfloor space. Gappy floorboards are ideal for this.
Otherwise, you could channel air through gaps between the skirting and the
floor.

Christian.

Thanks for these responses.

What if I were to use Knauf space blanket? It's on offer at B&Q right now.

This looks to fibre glass / mineral wool type roll in a relective blanked
enclosure. I don't have a link to it directly, but it looks simialr to
http://www.knaufinsulation.co.uk/out.../page_121.html




"JM" wrote in message ...
I have a 1930s house with the ground floor consisting of wooden floorboards
on timber joists. In turn, the joists are supported by brick pillars or by
the main walls. Under the floor there is a 2 foot high crawl space
ventilated by airbricks. There is access via several crawl hatches. The
underlying soil is dry to the touch.



I'm looking to insulate under the floor without removing the floorboards.



I've read about various possible approaches using rockwool / loft
insulation roll between the joists suspended by net / nylon cord /
battens, or alternatively using rigid panels of Kingspan / Celotex /
Floormate cut to fit between the joists.



Are either of these approaches sensible and practical, or are the any
alternatives? Or alternative products to use?



If I use rigid panels, I have concerns about creating a possible future
damp problem if I block up the end of this cavity/channel and air is
effectively trapped in a cavity between the underside of the floorboard,
the joists, and the rigid panel. If I don't block the ends of this cavity,
is it just a waste of time? Or should I push the rigid panel next to the
underside of the floor board?



Presumably I should not have insulation in contact or close proximity to
electric cables for risk of leaching chemicals from the cable insulation?



What are the possible options and suggestions?

JM wrote:
Thanks for these responses.

What if I were to use Knauf space blanket? It's on offer at B&Q right now.

This looks to fibre glass / mineral wool type roll in a relective blanked
enclosure. I don't have a link to it directly, but it looks simialr to
http://www.knaufinsulation.co.uk/out.../page_121.html



Not sure what its called but what about the rolls of "silver bubble
wrap" (great description!). They are apparently as good as the thicker
mineral wool, but i would imagine a lot less messy? Don't you just
staple them to the joists, so no messing around with nets and wires?

This sound like the same stuff. A silver space blanket enclosing fibre glass
/ mineral wool on a roll. Must less messy to deal with.


"Harris" wrote in message
oups.com...
JM wrote:
Thanks for these responses.

What if I were to use Knauf space blanket? It's on offer at B&Q right
now.

This looks to fibre glass / mineral wool type roll in a relective blanked
enclosure. I don't have a link to it directly, but it looks simialr to
http://www.knaufinsulation.co.uk/out.../page_121.html



Not sure what its called but what about the rolls of "silver bubble
wrap" (great description!). They are apparently as good as the thicker
mineral wool, but i would imagine a lot less messy? Don't you just
staple them to the joists, so no messing around with nets and wires?