What ceiling insulation do I need?

longwalks1

Currently replacing the kitchen ceiling, approx 20m2.  Adding fire rated GU10 led down lights.  The gaps between the ceiling joists/noggins currently stuffed with a layer of insulation, it’s texture/construction is somewhere between kingspan and the loose rolled stuff you find in the loft.  

I’d like to add more insulation, but what’s best to add another layer prior to fitting the new ceiling?  Joists are (I’m at work so guessing) 8” deep, and only looks like a 3” or 4” layer of insulation

tacpot12

It sounds like the existing insulation is in the form of batts. Semi-solid slabs of insulation fitted using friction between the joists.

So you basically want more of the same, BUT you need to be very careful you don't over fill the cavity. It sounds like you have a "cold roof". This is a very specific design of roof that requires ventilation (cold air) over the top of the insulation. If you block the cavity or holes through which the cold air enters or leaves the roof, you will cause the roof to fail within a few years. You need to research how "cold" roofs are supposed to work, and make sure you can idenfity where the ventilating air enters and leaves your roof before starting work.  

Bendy_House

Once you have sorted the insulation in between the joists - whether adding to these batts if space allows, or replacing them with a fully-rigid alternative (eg Celotex, which I understand would be more effective - snuggly fitted, gaps filled with foam, aluminium tape on joints), or even just keeping the existing batts if they're already pretty close to optimum - look at whether you can afford to lose an inch or two of ceiling height as well.

If you can, then it may be worth over-boarding the whole underside with an unbroken further layer of Celo/King, again foil taped, before p'boarding. 

If the LEDs need recessing, keep this to a minimum, and unbroken. They 'shouldn't' require ventilation, but check any clearance required.

longwalks1

tacpot12 said:

It sounds like the existing insulation is in the form of batts. Semi-solid slabs of insulation fitted using friction between the joists.

So you basically want more of the same, BUT you need to be very careful you don't over fill the cavity. It sounds like you have a "cold roof". This is a very specific design of roof that requires ventilation (cold air) over the top of the insulation. If you block the cavity or holes through which the cold air enters or leaves the roof, you will cause the roof to fail within a few years. You need to research how "cold" roofs are supposed to work, and make sure you can idenfity where the ventilating air enters and leaves your roof before starting work.  

Thanks tacpot12 - when you say cold roof do you think it’s a single story kitchen with a roof above it? Sorry I wasn’t clear it’s a 2 story part of the house and has a bedroom above the kitchen. Would the ‘cold roof’ bit still stand?  Or could I fit more batt insulation?  At present it’s probably only 1/3 of the depth filled

longwalks1

Sorry, just checked the current insulation, it is semi rigid, and held in by friction between the joists, but it’s texture is ‘drier’ and more rigid than the batt insulation I saw online, which is almost like slabs of loft insulation with an almost candy floss shedding texture to them. These sheets are firmer, if you pulled one out and stood it on it ends, it would fold over or collapse. Hope that makes sense 

tacpot12

I assumed that the insulation would be part of the roof, as you don't usually install insulation between occupied floors, unless it is for sound rather than warmth. The "cold roof" bit wouldn't apply if there is a heated room above. 

Is the insulation you are looking to add for sound insulation, or for warmth?

Bendy_House

longwalks1 said:

These sheets are firmer, if you pulled one out and stood it on it ends, it would fold over or collapse. Hope that makes sense 

They'd fold over if propped on their end, but can still remain flat in situ when horizontal? What mystical properties!

Anyhoo, your situation has always made me wonder; as Tacpot says, it's unusual to have insulation in between floors like this, since it's all within the fabric of the house, and - in theory - you don't need insulation there. A bit like you wouldn't put thermal insulation inside the internal walls between rooms.

So 'sound' insulation is a good bet, and the texture of the material might suggest this also.

However, I've always found it strange that there isn't thermal insulation in between floors, because I understood the floor/ceiling joists are very often open to the wall cavities - if not 'fully', at least via gaps - so I imagine there must have a howling travelling along them, between floors? Pretty sure the last house we had, where we stripped back the T&G floors upstairs, there was a darned obvious breeze coming up through it, so I ended up sealing all the joints with brown frame sealant (looked ok as the boards were stained mid-oak).

If the void is ventilated - intentionally or no - then it would thank you for some insulation.

Anyone know if the void is ventilated?

longwalks1

tacpot12 said:

I assumed that the insulation would be part of the roof, as you don't usually install insulation between occupied floors, unless it is for sound rather than warmth. The "cold roof" bit wouldn't apply if there is a heated room above. 

Is the insulation you are looking to add for sound insulation, or for warmth?

Oooh, I assumed for warmth, to keep heat downstairs as we will spend most of our time in the kitchen/dining area once finished.  We’re only ever about the kitchen when we go to bed, straight under the duvet.  Saying that though a competent DIY’er I work with suggested insulating the ceiling void but said to prevent sound from travelling.. and never mentioned heat loss through the ceiling to upstairs 

Bendy_House

Are you DIYing this work, LW?

Worth pricing up the difference between plain plasterboard, and - say - 35mm Thermal Laminate Board (P'board with an inch of high-quality insulation bonded to it)? Or, an inch of Celotex/Kingspan and then p'board - whichever is cheaper (and the latter would be better, if a little more work.)

If the cost difference is manageable, then it would be a belt-and-braces approach!

I am pretty sure that - whether designed to be or not - the ceiling-to-upstairs floor void in many houses have a fairly free flow of external air running through them.

Unless more knowledgable folk know better.

FreeBear

Bendy_House said: Anyhoo, your situation has always made me wonder; as Tacpot says, it's unusual to have insulation in between floors like this, since it's all within the fabric of the house, and - in theory - you don't need insulation there. A bit like you wouldn't put thermal insulation inside the internal walls between rooms.

So 'sound' insulation is a good bet, and the texture of the material might suggest this also.

As the ceilings on the ground floor are removed, I've been filling the voids between the joists with fibreglass insulation. Primarily to try and reduce noise coming through the floor/ceiling, and also to keep the heat in rooms downstairs. The insulation will also have a modest effect of reducing the speed at which fire spreads should anything untoward happen in the kitchen - On that count, best to avoid Celotex or Jablite type insulation boards.

A couple of points on LED lamps & insulation - The LED fittings do give of heat, and many of them are designed to operate in "free air". Blocking air flow could cause the lamp to overheat and shorten its life.

Bendy_House

FreeBear said:

A couple of points on LED lamps & insulation - The LED fittings do give of heat, and many of them are designed to operate in "free air". Blocking air flow could cause the lamp to overheat and shorten its life.

Yes, the installation instructions should always be followed.