Double Height Ceiling which insulation? Includes Downlighters

jasgrif11 · 25-10-2009 2:09pm #1

Hi All,

I'm currently renovating a bungalow and I'm drylining all the external walls and have upgraded the attic insulation to 400mm, however I have also built on a double height large kitchen/Dining room. The kitchen ceiling goes straight up to the roof and I was wondering what is the best insulation that I can use considering I will only have 6 inches between felt and slab?

Another issue is the kitchen will also have 20 downlighters and my electrician advised 6 inches of spacing around these for heat build up.

Any help is appreciated.

Thanks
J

teepee · 25-10-2009 8:19pm

hi ,
Its best to get fire boxs for the suppliers .

gman2k · 26-10-2009 4:11pm

Do you have sloped ceilings? and are the 20 downlighters built into the slope?
You'll have 20 cold spots in your ceiling so!

jasgrif11 · 26-10-2009 4:23pm

Yes they are sloped ceilings. Is there any other solution besides changing the light fittings? What type of insulation is the best for this purpose?

gman2k · 26-10-2009 7:38pm

It's the downlighters that's the problem (specifically the heat from the bulbs) that's the problem, not the insulation......
Now, you could create extra depth in the sloped part of the ceiling by counterbattening the rafters internally by say 50mm, and insulating this space also with 50mm PUR board or equivalent.
This would give you 200mm depth for the construction.
You could then back the downlighter voids on external side with 50mm insulation, to reduce the effect of the cold spot (created by the downlighter voids).
You could then form the light box void with 15mm plasterboard and seal all edges with intumescent mastic.
Finally, only then use LED down lighter bulbs, as they do not give out any heat, and won't pose a risk to your insulation.
However - whilst you as the current home owner - knows about this construction, and the need to only use LED bulbs, the next owner of your house may not....
The best solution is not to use downlighters in these sloped ceilings, to eliminate all fire risk and to maintain insulation integrity.
Have you thought about low voltage lights on rails/ wires - like what you may see in fancy restaurants? They are independent of the roof construction and look really classy!

exaisle · 26-10-2009 7:55pm

I can suggest two solutions: 1. There is insulation available which is about 5mm thick....it's aluminium clad polypropylene (really a 5mm layer of polypropylene in an aluminium foil sandwich). It is rather expensive by the roll but is far more efficient than standard insulation board or fibreglass, but youre unlikely to need anything like a roll. I had a similar issue with downlighters, so I left a gap in the standard insulation above the downlighters and effectively made "igloos" with it.

You didnt mention whether the downlighters are mains powered or low voltage? My second suggestion would be to consider using either cfl bulbs which dont get as hot as standard halogens, or LED bulbs...both are mains powered (although most cfl's can't be dimmed and no LEDs can).

E.

jasgrif11 · 26-10-2009 7:58pm

I'm thinking that the rail/wire lights are the only option. This house is going to be sold eventually so its would be too much hassle counter battening. I'm thinking 150mm Rockwool insulation then insulated plasterboard then light fittings that are surface mounted.

Has anyone installed these wire fittings or have other alternative fittings that may be similar to the recessed GU10's? I suppose something that looks good. I've searched a few online stores but haven't seen anything that looks good.

Mellor · 26-10-2009 10:26pm

exaisle wrote: »

I can suggest two solutions: 1. There is insulation available which is about 5mm thick....it's aluminium clad polypropylene (really a 5mm layer of polypropylene in an aluminium foil sandwich). It is rather expensive by the roll but is far more efficient than standard insulation board or fibreglass, but youre unlikely to need anything like a roll. I had a similar issue with downlighters, so I left a gap in the standard insulation above the downlighters and effectively made "igloos" with it.

Are you joking. The foil sandwich insulation has been proven to not work for sometime now (at least 3 years). The only people that used it were cowboys and people who didn't understand it. I don't know of any professional that would recommend it.

You didnt mention whether the downlighters are mains powered or low voltage? My second suggestion would be to consider using either cfl bulbs which dont get as hot as standard halogens, or LED bulbs...both are mains powered (although most cfl's can't be dimmed and no LEDs can).

you have you reasons for promoting CFLs I reckon.

OP, its a double height space, so ceiling height isn't an issue.
A regular ceiling with service cavity isn't going to cost much or take time. I can't see a problem with this solution.

As for the wire hanging lights. These are just like regular suspended lights, albeit with modern design touches

Lightning McQue · 27-10-2009 11:01am

Mellor

If the multi-foils are discredited how would you insulate the double heighted ceiling?

Assuming that you can't batten underneath the rafters could you use multifoils in association with another insulation product?

What insulation product would allow you to exceed the current building regulations?

Lightning

gman2k · 27-10-2009 4:13pm

Lightning McQue wrote: »

Mellor

If the multi-foils are discredited how would you insulate the double heighted ceiling?

Assuming that you can't batten underneath the rafters could you use multifoils in association with another insulation product?

What insulation product would allow you to exceed the current building regulations?

Lightning

How would you insulate the ceiling? - Easy 100mm rockwool, and leave 50mm airgap on felt side for ventilation. You will need ventilation along the ridge of the roof also.
The OP can batten below the rafters but by the sounds of it doesn't want the hassle!

To properly insulate this roof, and to prevent cold bridge along the rafters you should counter batten 50mm or 100mm and fill this void with rockwool also.
whether this meets or exceeds Part L, you'll have to ask your assessor or talk to Mr. Rockwool...

There is also the option of insulating over the rafters, which creates a complete warm roof, and the full 150 rafter void can then be insulated.
@ Lightning McQue - Forget about using multifoil as an insulation product on it's own, or with other combinations, as it will not work.
Having said that, I have used it in very minor locations to counter cold bridging where other insulations simply would not fit. That is not a recommendation from me!
There are other thin insulation products out there - Moy Materials Hunton board for example, and there is another very expensive product called AeroGel.

Mellor · 27-10-2009 10:42pm

Lightning McQue wrote: »

Mellor

If the multi-foils are discredited how would you insulate the double heighted ceiling?

Just like ant other roof, the double height doesn't change anything.

Rigid insulation over the rafters
Quilt (rockwool, glasswool) between the rafter (maintain 50mm airgap)
Rigid between the rafters, with or without an additional layer below the rafter betwen battons

gman2k wrote: »

there is another very expensive product called AeroGel.

Very expensive, not current used for walls and roofs, more suited to skylights and NASA projects.
But Aerogels are the worlds best insulator, this is a fact not an opinion.

jasgrif11 · 27-10-2009 11:28pm

Thanks guys. I think I will insulate with 100mm rockwool. Would it be a good idea to install insulated plasterboard under this. I will go for surface mount spots

onq · 30-10-2009 12:05am

jasgrif11 wrote: »

Thanks guys. I think I will insulate with 100mm rockwool. Would it be a good idea to install insulated plasterboard under this. I will go for surface mount spots

I'm not certain of the situation - because I've seen no drawings, but where the ceiling follows the roof the regs advise a 50mm vented cavity should be used running from eaves to ridge or whatever attic there is above the sloping section.

In addition to this you'll need continuous ventilation of 25mm at the eaves and 5mm at the ridge or their equivalent in discrete vent opes.

Insulation may be achieved by high density slabs cut to fit between the joists with a plaster faced slab with integral VC fixed to the underside of the joists. The VC joint between the vertical wall elements and the sloping ceiling elements needs careful consideration. VC = Vapour Check.

Down-lighters [DLs] are difficult to detail correctly. For example, structure is required to have a minimum of FR30 to facilitate escape from fire. A DL allows it to burn through in 15mins. How is the house compliant with Part B if the roof collapses on fleeing occupants within 10 minutes - it seems to me that it isn't.

Each D/L is a hole in the insulation.
Each D/L is a penetration that may allow structural timber elements to fail within 30 minutes in a fire emergency.

Separate from this the heat build up under insulation from either the lamps themselves or their transformers can lead to a fire hazard, but keeping the insulation back just worsens the insulation situation.
One means of mitigating the problems is to use an FR30 DL fire hood sealed to the upper face of the ceiling plasterboard finish with intumescent paste.
This will reduce heat transfer and maintain FR30 where required..
A final measure is to specify transformers that shut down in the event of heat build up.

Take note that I'm not endorsing these details for D/L's - my preferred solution would be spots on a track below fixed to the underside of the ceiling - my intention was to elaborate a litle on the problem and mention two workarounds.

HTH

ONQ.

gman2k · 30-10-2009 11:21am

Mellor wrote: »

Rigid insulation over the rafters

Quilt (rockwool, glasswool) between the rafter (maintain 50mm airgap)

Rigid between the rafters, with or without an additional layer below the rafter betwen battons

Mellor, if you are insulating with rigid over the rafters (on external face of rafter), then you don't need a 50mm air gap, as you are creating a warm roof structure.
It's just like warm and cold roof construction in flat roofs.

onq · 30-10-2009 12:21pm

gman2k wrote: »

Mellor, if you are insulating with rigid over the rafters (on external face of rafter), then you don't need a 50mm air gap, as you are creating a warm roof structure.
It's just like warm and cold roof construction in flat roofs.

My understanding is that what Mellor appeared to describe [and I haven't asked him to clarify, which I now do] was not warm deck insulation, in that the insulation was beneath the envelope, not above it or forming part of it.

It appeared to be a form of full-fill insulation for roofs, although how the insulation is to be fitted above the rafters is a little unclear to me. Specifying Rockwool only ensures the material itself will be unlikely to be affected by any build up of interstitial condensation that may occur.

I'm not sure of the acceptability of this kind of construction, except to say that opinions differ and conditions on the face of the timbers nearest the extenal envelope need ot ba carefully considered to avoid insterstitial condensation build up in the last 25-50mm of the "sandwich".

It doesn't matter if the insulation type is unaffected by interstitial condensation for the puposes of retaining heat [very important for recovery once conditions change]. Once its holding moisture, thermal performance suffers hugely.

My understanding is that closed cell insulation offers advantages over Rockwool in this regard, but still leaves the "outer" face of the timbers at some risk unless the 50mm ventilation gap is maintained.

The 50mm vented gap is intended to create conditions where any build of interstitial condensation is disffused in a free flow of air. I am not aware of how well "breather membranes" support full-fill detailing an Irish climate [as opposed to say, the South Counties in England, reputedly a difference place altogether].

So please correct me on this if you think I am in error in what I've said.

Mod, please feel free to move to another thread if appropriate.

FWIW

ONQ.

RKQ · 31-10-2009 11:05am

The OP should seek professional advice. ould also post a photo to clarify the current construction.

I assume the roof structure, felt and slate / tile is complete so the OP should state wheather it is Warm Roof or a Cold Roof - Gman2k makes a valid point regarding Warm Roof construction. Breathable felts and counter battening are also important.

IMO 150mm thgick fibre glass insulation, running the slope of the roof is not enought to comply with Building Control. The OP is advised to improve on this and consider Kingspan / Xtratherm etc.

Downlighters are not a good idea IMO - cold spots, risk of fire, running cost, potential future tax. There are many attractive alternatives on the market. LED is a good idea.

onq · 02-11-2009 9:35am

RKQ wrote: »

The OP should seek professional advice. ould also post a photo to clarify the current construction.

<nods>

I assume the roof structure, felt and slate / tile is complete so the OP should state wheather it is Warm Roof or a Cold Roof - Gman2k makes a valid point regarding Warm Roof construction. Breathable felts and counter battening are also important.

The OP may not be familiar enough with the various kinds of build up to state one way or another.
Gman2k makes a very odd point about placing kingspan insulation over the joists on what we assume is a traditional slated roof - what are the slates fixed to?

IMO 150mm thgick fibre glass insulation, running the slope of the roof is not enought to comply with Building Control. The OP is advised to improve on this and consider Kingspan / Xtratherm etc.

Kingspean offer the detail I outlined above - cut insulation between the joists [say 124mm between 175mm joists giving the 50mm air gap] with an additional plaster faced warmboard below the joists to make up the required total depth.

Downlighters are not a good idea IMO - cold spots, risk of fire, running cost, potential future tax. There are many attractive alternatives on the market. LED is a good idea.

Hadn't considered the LED option. Perhaps they are small enough in the event of a fire not to permit passage of flame, or cold smoke and gases earlier in the fire's propagation, but I suspect not.
I'd be surprised if you can seal them properly and the myriad points may be just what a fire needs but I cannot be definitive on this.
It may be they need a false ceiling to be safe - something like an impervious ceiling above, with 1200x2400m sections of timbers or self finished plasterboards on 50mm battens pre-wired offered up to it might work.

FWIW

ONQ.

gman2k · 02-11-2009 11:04am

onq wrote: »

<nods>

Gman2k makes a very odd point about placing kingspan insulation over the joists on what we assume is a traditional slated roof - what are the slates fixed to?

ONQ.

Nothing odd.... slates are still fixed to battens!
Rafter,
External rigid insulation,
Breather membrane felt
Counter batten (in line with rafter) - this is where you need particular fixings down through the insulation and into rafter.
Batten,
Slate.

Then fill rafter void with insulation and voila - warm roof!

onq · 02-11-2009 11:35am

gman2k wrote: »

Nothing odd.... slates are still fixed to battens!
Rafter,
External rigid insulation,
Breather membrane felt
Counter batten (in line with rafter) - this is where you need particular fixings down through the insulation and into rafter.
Batten,
Slate.

Then fill rafter void with insulation and voila - warm roof!

Ikay, I'm not being dogmatic about this, but this seems odd.
Lining up counter-battens with rafters through a layer of rigid insulation seems optimistic - I think you might have to fix the insulation in modules of the rafter spacing, to allow the roofers or whever's doing this to feel the edge of the slabs.
Fixing the felt/breather membrane should occur directly onto a firm substrate, with a pressure joint through a firm substrate, like fising to rafters with bettens on top - this prevetns water ingress through the penetrations.
I'm not sure fixing through the felt resting on the insulation will do this - you may end up with multiple penetrations that are not effectivel ysealed in this way.
While rigid insulation can take a distributed load from say paving slabs, its not designed to support mechanical point loads with a lateral element - i.e. slate fixings on a sloping roof.
Normally slates get fixed to a firm substtrate - like timber battens on rafters or battens to counter battens onto rafters - without any "squidgy" [highly technical term] materials in between.
I'm also not familiar with a fixing detail that would allow safe transmission of loads, particularly wind loads, to the roof structure., where its fixed through say 100mm insulation [you didn't specify the depth, so I'm guessing].
But I'm always willing to learn.

If you've a detail of something done this way I'd really appreciate a look at it.

TIA

ONQ.

PS Muffler, this is a technical discussion about warm roofs in a thread about insulation - it is anything BUT off topic.

RKQ · 02-11-2009 12:56pm

onq wrote: »

Gman2k makes a very odd point about placing kingspan insulation over the joists on what we assume is a traditional slated roof - what are the slates fixed to?
ONQ.

Rafters - long screws or special fixings by a well known manufacturer! I have 25mm Kingspan on top of my rafters and counter-battens. Its a standard detail - used by "most" breathable felt manufacturers. It may also give a better u-value. It certainly gives a better internal celing height, should you wish to maximise the amount of exposed truss / purlin in a roof.

There are many ways to insulate this type of roof, hense my advise to the OP to seek professional advice on their particular requirements.

onq wrote: »

Hadn't considered the LED option. Perhaps they are small enough in the event of a fire not to permit passage of flame, or cold smoke and gases earlier in the fire's propagation, but I suspect not.
I'd be surprised if you can seal them properly and the myriad points may be just what a fire needs but I cannot be definitive on this.
ONQ.

Hoods can be purchased at any electrical retailer to prevent firespread from a spot light. The heat generated from a spot light could cause a fire in the ceiling. I was not making reference to the lights allowing flames into the ceiling or permitting passage of flame. I suggested LED as they give off very little heat and are less lightly to ignite the (PIR) insulation.

As I stated above "IMO 150mm thick fibre glass insulation, running the slope of the roof is not enought to comply with Building Control." Additional insulation will be required.

I have no problem giving free advice or expressing an opion on Boards, if it helps an individual. It is up to the OP and all Readers to agree or disagree with all opinions expressed on this site. All opinions are valid. However, I do believe the OP should seek Professional advice on this particular issue.

I have to agree with ONQ on his / her final point - it is an interesting topic!

Insulation over & between Rafters:-
http://www.quinn-therm.com/roofinsulation/above-rafters.cfm

http://www.insulateonline.com/index1.htm?pitched5.htm~main

http://knaufinsulation.co.uk/selfbuildinsulationcom/self_build_solutions/roofs/pr11-between__above_rafters.aspx

jasgrif11 · 02-11-2009 6:46pm

This is the option I'm thinking of. under the felt I plan to put cut kingpsan with a 50mm air gap. Then apply a standard slab. Then counter batten to 4inches below then install an insulated slab. I will then have 21 recessed lights in the insulated slab.

I know I here everyine saying no to recessed lights but herself wants them. I plan to put in the Gu10 CFL blulbs.

Does all this sound ok? I know I will have issues with air tightness having so many recessed lights but its a big area. Is 4 inches of space enough between both slabs?

murphyep · 19-11-2009 7:41am

Hello,
Just wondering which is better for roof insulation:

cellulose(blown in) or rafterloc?

Cheers,
Eddie

Double Height Ceiling which insulation? Includes Downlighters

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