Undercroft Insulation?

[Time Waster]

We've got wooden flooring in our living / dining room. Getting rid of carpet loses insulation by a surprising amount. So the undercroft below we intend to insulate. What's the best option?

There's lagged pipes and cables. Not much headroom. I'm thinking that's either slabs, wool or something more clever involving foil, bubble wrap thin layer insulation instead.

Any recommendations?

 

[Beebo]

When you say undercroft. Are you referring to the void below suspended floorboards which allows air to move under the building?

I have a similar problem but the void is only about 18 inches deep so it’s impossible to get access unless we rip up the floorboards.

 

[Time Waster]

No, it's a bit more than that. One end of the house has a garage under it, the other is the undercroft with the ground rising up to that end and back of the house. It's about half height for me, but I am tall. Plenty put storage room under there including bikes.

 

[Beebo]

A basic option is a roll of fibreglass wool and chicken wire to hold it in place.

 

[SpokeyDokey]

No, it's a bit more than that. One end of the house has a garage under it, the other is the undercroft with the ground rising up to that end and back of the house. It's about half height for me, but I am tall. Plenty put storage room under there including bikes.

Similar-ish here.

We are built into the side of a hill.

We have a carport & adjacent spare room (used as a gym) under the house. The carport in turn leads to the garage cum secondary utility area.

The carport & gym are insulated between their respective roof and house floor with 300mm thick insulation roll. Importantly this means that the only area of flooring that is over 'open air' ie the carport, is properly insulated.

The balance is uninsulated but warmed with the house boiler (oil fired) sited in the garage which keeps it from getting too cold under the floor of the rest of the house.

We decided not to put slab insulation under the rest of the house as a) not much heat goes downwards and b) it would interrupt airflow from the airbricks which, if blocked, can cause a whole lot of problems in itself

 

[Time Waster]

Quick question, do you need a vapour barrier with the insulation? I saw a video where the guy put a layer of plastic them the insulation nslab between the rafters under the floor. The plastic extends down the sides of the insulation too.

I'm guessing if you insulate the effect is to have the gradient in temperature not in the floorboard depth but through the insulation with a warm space above the insulation. This is warm and moist air which could condense in the insulation wetting it out. Is this correct?

 

[Gillstay]

I put slabs of 3 inch thick Kingspan between the joists and then secured them with long nails tapped in each side, though chicken wire as suggested would do the same. Worked well.

 

[Time Waster]

Is that foil backed?

 

[Ian H]

We used 4" Kingspan type sheets between the joists in our cellar. I might add another 2". The cellar is well-ventilated and needs to be, so the rooms above require insulation.

 

[Gillstay]

Is that foil backed?

Yes it was.

 

[slowmotion]

If you can get access to the joists and decide to use rigid insulation, it's worth gunning in a small amount of foam at the joist/insulation junction to prevent cold air getting through any gaps.
Buy a cheap foam gun and use Low Expansion Soudafoam cans.

This stuff doesn't piss everywhere when you release it and it's easy to control when filling narrow gaps, unlike most PU foam......

 

[CXRAndy]

Cold floors or suspended floors with no insulation can make the building much colder.

Remedial works to insulate can involve fitting foil back panels between the joists, involves lifting some or all of the flooring, to jack hammering whole hard floors out, digging down, back fill add DPM 100-150 insulation. Whilst your there add underfloor heating system then 75 mm of flow screed

 

[Time Waster]

Undercroft access so no need to lift a floor up.

In my old job I might have had the opportunity for knauf slabs to fall out of the warehouse into my van. Same with Al foil backed glass fabric which would have made a cheap solution that could have worked. All 455mm width. Being fairly soft and flexible it would have filled any gaps due to uneven joists. Oh well, looks like I'll have to pay up now.

 

[Gillstay]

If you can get access to the joists and decide to use rigid insulation, it's worth gunning in a small amount of foam at the joist/insulation junction to prevent cold air getting through any gaps.
Buy a cheap foam gun and use Low Expansion Soudafoam cans.

This stuff doesn't piss everywhere when you release it and it's easy to control when filling narrow gaps, unlike most PU foam......

Yep worked well om my job. Good advice.

 

[bruce1530]

North of the border, you can get a 75% grant (not means tested) for loft insulation and underfloor insulation. I know of 3 people (including my daughter) who have had it done recently.

There is about 2 and a half foot space under her floor, maybe slightly more, so space to crawl. From the trapdoor in front room, you can squeeze through various gaps and holes and get under all the rooms.

On the appointed day, the van turned up loaded with rolls of glass wool. 3 surprisingly tall guys, wearing overalls, gloves with cuffs taped, and face masks, went under the floor, with the rolls of insulation, nylon netting and staple guns.

Took them most of a day. Glass wool between joists, tacked in place with staples, then netting underneath, again stapled, to hold it all in place.

Makes a noticeable difference.

Chatting to the guys on their break, they said ours was an easy job, as there was plenty headroom. I asked what was the minimum they would work in; they said 18"