Advice for insulating cellar

[msparker]

I live in a Victorian house. The previous owners did a lot of work to make it warmer and more eco e.g. Double glazing, some external wall insulation, underfloor heating in most of the ground floor. One area that seems like a big omission though is that they didn't insulate the cellar ceiling / ground floor. The wooden floor in the hallway is gappy so the cold from the cellar makes the hallway and in turn lots of the house cold! I'm thinking of chucking in some insulation in the cellar ceiling but have a couple of questions...

1) should I put PIR or something else? E.g. rockwool. Any particular thickness or anything?
2) do I need to do anything to ensure the house / cellar has sufficient ventilation or am I good to proceed? There is an airbrick at the front of the cellar but nothing else

 

[msparker]

Having had a proper look at the cellar, there are a lot of wires, nails, wonky bits. I'm thinking a flexible insulation will be the way to go. Id still love any advice on what is likely to work best in this environment and any advice on ventilation/avoiding problems due to humidity. I only have an airbrick at one end which I imagine isn't ideal

 

[woodieallen]

Carpet. Sorted.

 

[Sachakins]

Is it a full height cellar?

 

[msparker]

Is it a full height cellar?

It's about 6 foot high. 1.4m wide, 7ish m long

The latest thinking is to put mineral wool up. Hold it up with some webbing or perhaps some weed fabric I have which I think would work well (breathable). No additional vapour barriers etc. it seems like ideally I would have a vapour barrier on the warm side, but it'd have to go over the joists meaning the floor boards would need to come up. I have no intention of doing this, just putting insulation in from below, so a vapour barrier isnt feasible. So I'll go without, keep everything breathable and check it every now and then

 

[Sachakins]

Agree, but I would use chicken wire instead of weed fabric. It won't sag over time as the weed fabric will.

 

[Jester129]

Staple the weed fabric in numerous places to the underside of the joists?

 

[Cabinetman]

I’ve seen the insulation held up with short lengths of stiff wire sprung in between the joists. They are sold over here for just this purpose but I don’t know what they’re called -sorry.

 

[Katomi woodsmith]

I would put in ventilation and extraction in esp if you plan to use the celler
Definitely fit a co2 detector, fit it low down
Think of co2 like water, it will sink to the lowest point eg your celler.
Only you can’t see or taste co2

 

[cemannion]

Celotex or other make of PIR 25mm will provide sufficient and you only lose minimal head room. You seal the edges with spray foam. You can buy it bonded to plasterboard (try to get Moisture resistant) which then gives you a decoratable finish and is fire resistant. You can even fit recessed lights.
Walls as well perhps?

 

[msparker]

Thanks for the tips folks. I rolled up my sleeves and got it mostly done yesterday. I've put up mineral wool between the joists held up with a breathable membrane stapled to the joists. I've taken some moisture readings from the joists and have a humidity meter arriving today. I intend to monitor it all for a while to check things aren't getting more damp/humid. During the process I found the airbrick was pretty blocked and have now cleared it, so I'm hoping if anything it might trend a bit drier in the cellar and warmer in the house