Sheep Wool between joists under floor

new_owner

fluffpot wrote: »

Beware sheep's wool! A client of mine had to have the WHOLE house re-insulated, re-plaster boarded, plastered and decorated because of a moth problem - they came from the sheep's wool used in all walls as eco insulation....

I thought the wool was treated to stop this?

Carpets can also cause the same issue

"1.3.2 Borax: A naturally occurring, non volatile salt, Borax is used throughout the construction industry due to its many inherent advantages. Borax used in Sheep Wool Insulation acts primarily as a pest-repellent by inhibiting the development of beetles, moths, ants and cockroaches. Borax is practically non toxic to birds, fish, aquatic invertebrates, and relatively non toxic to beneficial insects. Borax also enhances the fire rating of construction materials as well as preserving the materials over time.

BlueC

Hi new_owner

Your question is of great interest to me as we're in a very similar position. I read this very question being answered by Jeff Howell in the Sunday Telegraph in January this year (link).

This is his response:

The best thing to do would be to insulate below the floorboards. Your son is fortunate in having the space to do this from below. The best material, although also the most expensive, is rigid PIR foam board insulation (Kingspan, Celotex and some builders' merchants' own brands). This can be cut to size with a saw, to make a tight fit between the floor joists, and pushed into place from below. A few galvanised nails in the sides of the joists will guard against it dropping out.

The ventilation of the subfloor void should come from airbricks in the front and rear walls, which your son should make sure are unobstructed and able to provide a through-flow of air. This is vital to prevent water vapour from the ground causing a build-up of humidity, and potentially contributing to wood rot in the floor timbers.

Underfloor insulation makes a fantastic difference to the comfort and fuel efficiency of any home.

What I still don't understand here is the apparent contradiction of advising to fill the space between the joists with insulation, and then saying the airbricks should allow a through-flow of air to the subfloor. I don't get it.

Surely if the spaces between the joists are filled then this will prevent the flow of air to the subfloor? Seems contradictory to me.

new_owner

Hi BlueC

This was the path that I started down with solid board insulation. But reading more the better approach seems to be a wool or similar hygroscopic material.

There are some good articles including the English Heritage one that points to using sheep's wool in older buildings.

They say as long as you have a breathable membrane to hold the insulation then there will not be a damp issue (wire mesh should do ) I have seen felt used when working from above. I am sealing the gaps between the boards with this black rubber tube stuff and so that seems to work well.

I have found that B&Q sell a sheep wool insulation which is 55% wool, 35% plastic bottles and 10% binder (Rubber and salts etc) and seems to tick the boxes and is cheaper than other makes. As soon as it opens tomorrow I plan to go and buy 4-5 rolls and some mesh and do the floor... If it goes ok then I will buy enough to do the house...

Edit. Does anyone know why the different amounts of wool content? some have 55%, 85% or 90+% is this a cost saving? does it make a difference? except the R rating is higher on the higher %.

new_owner

OK..

I don't recommend using the eco sheep's wool from B&Q...

Bought 10 rolls of the stuff and installed a one in the floor joists and kept an off cut to one side.

The rolls state that it will reach full height after 5 days (100mm). After 5 days it had not increased from the 50mm it came out of the pack as..

returned the whole lot today for a full refund (including the installed one).

Back to the drawing board on this project. I don't want to buy it another wool product online to find the same problem but then have to pay to return it.

Gloomendoom

Why not just use solid board insulation or even reflective foil?

We have an unheated cellar under my dining room and I haven't bothered insulating the floor. It's cosy enough as it is.

If you have solid 9" brick walls, I would devote most of your energy/money to insulating those. If you are prepared to lose a couple of inches of interior space, you will make a huge difference to how fast the house cools down when the heating goes off.

I have attended several seminars on caring for old houses (ours is 100's of years old) and the advice on insulation and preservation is contradictory. On one hand you will be told to stop up every gap to prevent heat loss and then, on the other hand, you will be told to maximise ventilation to prevent damp and rot.

new_owner

Hi Gloomendoom

I have looked into insulating the walls the trouble is the original plaster coving.

I have costed up Kingspan themafloor boards and the cost is around £250 (12 boards delivered) for 50mm (rising quite quickly if you go to 75mm or 100mm)

for the price I might just stick some solid board under the floor and monitor for any damp.