Partial loft conversion - insulation issues

Bendy_House

Brebal said:

The bedrooms below - one is at front of house, one at back. One is half the size of the other. I hadn’t known there was a way to insulate the ceiling from the underside. 

The eaves access is only on that one side.  There’s insulation in there but not very good. Basically a roll has been thrown in. Got quotes £200 to sort that. Wonder if I could do it myself tho. 

I think it was just flat boards under the carpet tiles. I could take the carpet up and lay some insulation board down if it would help, and be ok to walk on. I’d only have about an inch though before it affected the cupboards opening. 

It's easy to add more loft insulation, but I suspect it won't be very effective unless you can do the whole floor and not just the eaves area, and that might mean having to lift it first. If the eaves hasn't been floored, it should be possible to look under the loft floor from the side? And insulation in there?

If you do decide to add a layer of loft insulation over what's already laid in the eaves area, then ensure you don't block the outside eaves edge, as this is where these voids get their ventilation from, which is essential to prevent condensation from forming. If you post a photo of what's in there, we can guide you on this.

Tbh, adding a further roll of loft insulation in that one stretch of eaves space is unlikely to be noticeable. Yes, it's totally possibly to add insulation to ceilings from below, using insulated plasterboard as mentioned before. This will be very effective, as it'll be a full, unbroken layer of high-value insulation, going from room wall-to-wall.

If the walls have been cavity-filled, they should be decent too. If an external wall - especially if it's north-facing - is clearly colder than others, eg if you get signs of condensation or mould in corners, then these can be insulated in the same way, but it tends to be more effort as you have to work around windows, remove skirtings etc. 

That just leaves draughts to sort! Do not underestimate the effects of this. Really worth testing with a smoking taper, either side of the closed door at floor level. Try again when it's a bit windy outside.

markin

You need to know the depth of insulation you already have under the floor and in the rafters, You could pop the lights to get a look in there if you cant see it from eve, Then we can work out how much more you need to add.

 But with this years energy cap being estimated at £3000 a year for average use, And your unlikely to be average,  What is your current yearly estimate in kwh? It should say it on the bill.   It really may be best to just rip out the knee wall plaster yourself and put rolls or 100mm foam down over all.

Brebal

You’re all being really helpful!  Thanks. 

I’ve been in the eaves. It’s a bit draughty in there! There is insulation on the knee wall. Looking underneath and back into the room, there’s a three inch gap under the floor. I can see some insulation under there. I’ll add pics. 

I’ve got two inches of space before I get to the cupboard door. So wouldn’t I just be able to put insulation board down on top of the floor (just lift carpet tiles and re-lay)? Only because I can do that myself. If it’s not worth it I’ll look at other options mentioned m

Brebal

markin said:

You need to know the depth of insulation you already have under the floor and in the rafters, You could pop the lights to get a look in there if you cant see it from eve, Then we can work out how much more you need to add.

 But with this years energy cap being estimated at £3000 a year for average use, And your unlikely to be average,  What is your current yearly estimate in kwh? It should say it on the bill.   It really may be best to just rip out the knee wall plaster yourself and put rolls or 100mm foam down over all.

My yearly estimate is 3000kwh elec and 12500 gas

Bendy_House

Brebal said:

You’re all being really helpful!  Thanks. 

I’ve been in the eaves. It’s a bit draughty in there! There is insulation on the knee wall. Looking underneath and back into the room, there’s a three inch gap under the floor. I can see some insulation under there. I’ll add pics. 

I’ve got two inches of space before I get to the cupboard door. So wouldn’t I just be able to put insulation board down on top of the floor (just lift carpet tiles and re-lay)? Only because I can do that myself. If it’s not worth it I’ll look at other options mentioned m

It's draughty in the eaves? Good! That will keep it dry - very important.

Can you lift the carpet tiles, add a layer of insulation board, and replace them? Yes. That will help to keep the loft area 'warm', but really only if you add a heater - ie insulation doesn't create warmth!

The person who did this work added loft insulation to the walls, and then a layer of p'board to the eaves side. That, again, will help keep the loft room warm - if, again, heat is added. (I guess even body-heat will do this to some extent).

There is, however, a gap under the loft floor, and that means there's zero insulation to the ceiling of the rooms below. Two things you can do - you can try and stuff that space with loft insulation, and that might help a bit, but it'll always only be a 3" layer max, and that isn't much (in terms of 'loft' insulation). There will also be a constant through-draught of air percolating across there, which will reduce the level on 'insulating' a bit more. So, it should help the rooms below, but be nowhere close to a cure. If the rooms below are genuinely hard to keep warm, then I know what I would do, and that would be to line the ceilings with insulated p'board - 1 or 2 inches - and also make darned sure there are no draughts coming up through the bedroom floors and skirtings. The easiest way is to put down a layer of insulating fibreboard underlay, and seal around them.

This will not bring these rooms up to current regs, but it should make a very noticeable difference, and not cost that much. The alternative involves some seriously disruptive work. (Eg, your loft floor joists appear to be only 3" deep? That would need changing...)

I'd treat the two storeys as separate entities, and deal with them separately too.

Brebal

Ok, that makes sense. Thanks very much! I’m not bothered about the temperature in the loft, I just want to keep the heat in the house and be able to warm it up efficiently as I can. 

When you say insulation boards in the loft would keep the loft warm, I thought it would be the other way around, that the insulation would stop the heat from the house getting up to the loft. 

Doing the bedroom ceilings sounds good instead though. 

What kind of tradesperson would I need? 

markin

Just fixing all the gaps and under the floor with that roll will make a difference, use a stick to push it in, Do Insulate the hatch. Then 100mm board could then be added to the knee walls on the inside and top up the eaves with 100mm rolls. Then between the floor and sloped ceilings you would have at least a 200mm envelope.

You will have to make a hatch to get in the other eave or its all a pointless.

All of this is DIY possible, You just a cordless drill/driver 150mm screws for the insulation boards, 90mm screws to make a new frame and hatch, wood saw, a utility knife to cut the insulation.

I would leave insulating from the room below as a last resort as its the most disruptive and expensive with getting it plastered.

Bendy_House

Brebal said:

Ok, that makes sense. Thanks very much! I’m not bothered about the temperature in the loft, I just want to keep the heat in the house and be able to warm it up efficiently as I can. 

When you say insulation boards in the loft would keep the loft warm, I thought it would be the other way around, that the insulation would stop the heat from the house getting up to the loft. 

Doing the bedroom ceilings sounds good instead though. 

What kind of tradesperson would I need? 

There is a ~3" gap between the bedroom ceilings and the loft floor? (Are you sure it isn't more?) So, your bedroom ceiling is currently not insulated at all in that area - it's no surprise the bedrooms are hard to heat. 

If you add insulation boards to the loft's FLOOR, then that will help to keep heat inside the LOFT, but won't help the bedrooms at all. As Markin says, you'd need to STUFF the gap there with loft insulation in order to help 'both'.

Even then, if it's only a 3" gap, then it'll only be 3" of loft insulation - not much.

A different issue - caution with pushing insulation up the sloping eaves gaps, as cutting ventilation there could cause serious issues. You NEED a vent gap immediately under the ROOF!

Brebal

All I know about the three inches is from when I looked under the loft floor from the eaves. Sticking a tape measure down (where you can see the cables laying) is three inches. Whether there’s another layer under that I can’t see I don’t know?

I am thinking now it’s not that big of a job to take up the carpet tiles, unscrew the boards and put more insulation down (new and better stuff maybe), make sure it’s all filled.  I did wonder if i can just screw on some more 2inch high wood batons onto the joists and then have a 5inch gap to insulate, and just replace floor on top. Don’t know if that would be stable and strong enough to walk on though. 

(I’m quite capable of cutting wood, screwing and unscrewing etc. )


I don’t think I’m fully understanding the physics though. Why would underfloor soft insulation work to keep heat in the house below, but insulation board would heat up the loft? Only if anyone can be bothered explaining…

 

markin

If your capable of it then yes take the floor up and use metal plates on both sides about every ft to mate a 2x5 on top to get a good depth. The photo made it look like it was taller than just 3in.

This threads a little out dated but I would use some 170mm screws and plates.
https://www.diynot.com/diy/threads/strengthening-loft-floor.326918/