Insulating suspended flooring, without lifting floorboards!

Sharkford

Hi,

I'm trying to find out a solution for insulating my suspended flooring without lifting the floorboards. My house is a 1930's mid terrace that has a crawl space and due to the water table level, there is some pooling water in areas.

I'm going to insulate using mineral wool between the joists with a breathable membrane stapled underneath with wooden battens for security should the staples fail. I'm using mineral wool for the vapour permeability advantages due to the water pooling.

My question is, can I apply a DPM, on top of my floorboards? I want to then apply a carpet with underlay.

I.e. Carpet> underlay> DPM> floorboards> insulation (between joists)> breathable membrane> wooden battens.

Or should I leave the DPM and just add a decent underlay maybe that gold sided underlay and then carpet. I’m afraid of creating interstitial condensation.
Really appreciate the help!

grumbler

Well, I am no expert, but it makes no sense to me to put DPM over the boards and breathable membrane under.

IMO it makes much more sense to put DPM under the joists to protect all wooden parts from moisture.

Regarding the water, did you think about some digging to collect it in one place and installing some automatic pump?

Shaun_of_the_Dead

DPM over the floorboards will keep the carpet and underlay dry up to the point you fall through the floor.

FreeBear

Sharkford wrote: »

I'm trying to find out a solution for insulating my suspended flooring without lifting the floorboards. My house is a 1930's mid terrace that has a crawl space and due to the water table level, there is some pooling water in areas.

1930s build - Probably 3"x2" joists if it anything like mine. Be very careful not to block airbricks and make every effort to ensure there is a free flow of air across the full width of the floor. Personally, I wouldn't bother with a DPM. Unless you use a felt or wool underlay, most of them will act as a DPM to a certain extent.

king132

So...you don't want to lift the floorboards up but want to crawl underneath your floor, lay flat on your back on the left over probably damp rubble. Put mineral wool insulation throughout the floor, staple a membrane throughout and then batten the whole thing while on your back??

lg13mza

king132 wrote: »

So...you don't want to lift the floorboards up but want to crawl underneath your floor, lay flat on your back on the left over probably damp rubble. Put mineral wool insulation throughout the floor, staple a membrane throughout and then batten the whole thing while on your back??

That's what I did. I wouldn't wish it on my worst enemy.

markin

A piece of osb to lay on would make it nicer.

Mistral001

I would not put a DPM on the underside of the joists but insure that the void is well ventilated. If the void is well ventilated the joists should not rot. If you do not get the DPM sealed 100%, then moisture could be trapped in the space between the DPM and the floorboards and cause the joists to rot. It also could contravene the Building Regulations since the joists would not be ventilated. However my main worry would not be the Building Regulations, but the risk of rotting joists.