Insulating under a suspended timber floor

[Bewdy]

Hi, I have a 1890’s house which has a cellar under the entire house (currently under 6” of water, but that is a different issue). The house is always cold and costs a fortune to run, so I am wondering how best to insulate the ground floor, which is a suspended timber floor. Currently I will need to remove patchy lathe and plaster which is still in place in parts of the cellar.

Given the issues with damp in the caller I am concerned about making damp and moisture worse in the ground floor structure and creating condensation.

What would be a sensible approach to adding insulation to the floor. Do I need to make it very breathable? I’m assuming I need to steer clear from going nuts with draft proofing to assist ventilation in the floor cavity?

 

[23vc]

100mm (or thereabouts) PIR in between the joists as long as it doesn’t obstruct any air bricks?

 

[Lower]

Concentrate on the ceilings and walls. If you have carpet and underlay, you’ll notice no significant benefit from insulating the floor. I speak from experience.

 

[Bewdy]

Concentrate on the ceilings and walls. If you have carpet and underlay, you’ll notice no significant benefit from insulating the floor. I speak from experience.

Thanks, but we do t have carpets and underlay. We have wooden floors.

Walls have been cavity filled. The roof has been converted into a loft and is well insulated. We have 3.3m tall rooms, so the last place to tackle is the floor.

 

[Jurassicspark]

Concentrate on the ceilings and walls. If you have carpet and underlay, you’ll notice no significant benefit from insulating the floor.

From your perspective, you may not. However, your bills will significantly reduce, along with your EPC.

 

[jono_h]

I just used loft insulation between the rafters, and stapled roof membrane to the bottom of the rafters. But plenty of underfloor ventilation is key.

 

[Lower]

From your perspective, you may not. However, your bills will significantly reduce, along with your EPC.

Our heating bills didn’t reduce in any noticeable way.

The suspended floor needed replacing due to rot, but insulating it was a waste of money in my opinion.

 

[Bewdy]

Our heating bills didn’t reduce in any noticeable way.

The suspended floor needed replacing due to rot, but insulating it was a waste of money in my opinion.

Well it’s all relative. My concern is that (although heat rises) we are heating this very large dead space underneath our house, by virtue of the fact that there is only wood boards for insulation between the floors. Access would be relatively easy for me to fit the insulation, so it is just the material cost and bit of effort. But I don’t want to create a moisture problem.