Proper Downlights / Airtight

[Onoff]

Just about to puncture in earnest my lovely plasterboard ceiling for 5(6) downlights and in particular the continuous vcl that sits above the moisture resistant plasterboard.

 

I've had it planned to do like this for a while but will my idea to maintain the airtight layer work? 

 

So, between the joists its fully filled with 100 + 50mm of foil faced PIR. I'm using TH140 Thermahood downlight covers that measure 185 x 185. A rigid plastic type they are. They have no bottom flange really as per the sketch (the circular ones do but I like squares). So I drill up from below my 60mm dia hole that goes through the plasterboard, vcl and into the foil faced PIR a bit. Then with a long series pop a hole up through the PIR. Into the loft with my 200x200 wooden jig, centre over the hole and neatly cut out the PIR. At this point I have the opportunity to LEAVE the bottom layer of foil intact as the PIR just peels away. That is above the vcl. Ideally though I want the vcl outside the 185x185. So I cut back an exact 185x185 section of foil and vcl and centre the Thermahood over the cut out. I figure just a bead of intumescent sealant around all 4 sides should do the trick or should I invest in some airtight tape? To maintain the insulation I'll be adding a 150mm deep slab over the hole area above the downlight. Plenty of height to do so in what is dead space. There's a good 300mm between the tops of these ceiling joists and the underside of the dormer extension floor joists.

 

Do I need to fill the void outside the tapered sides of the Thermahood? Low expansion foam maybe? Or can I leave this void unfilled? Thinking condensation maybe? Cheers.

 

 

[MikeSharp01]

2 hours ago, Onoff said:

Do I need to fill the void outside the tapered sides of the Thermahood? Low expansion foam maybe?

Off the top of my head I think I would say yes because you want to keep air circulation / convection, even in a small space, to a minimum. Not sure I would use foam, might go for glass wool - easier to manage.

[ProDave]

I think you would struggle to get airtight tape down into that narrow gap.

 

I would stick the vcl down and stick the hood in place with something like "sticks like...."  then foam around the hood with expanding foam, leaving the top of the hood exposed.

 

Assuming LED lamps no heat problems.  Make sure you seal the cable entry into the hood.

[Dudda]

Cut back the foil to 200x200mm but leave the VCL 185x185 or smaller if you can. You should have 15mm now of exposed VCL. Use an airtight mastic like Orcon-f to fix the hood to the VCL. Don't use silicone or foam and don't fix the hood to the foil. It should be fixed to the VCL.

[Onoff]

23 minutes ago, Dudda said:

Cut back the foil to 200x200mm but leave the VCL 185x185 or smaller if you can. You should have 15mm now of exposed VCL. Use an airtight mastic like Orcon-f to fix the hood to the VCL. Don't use silicone or foam and don't fix the hood to the foil. It should be fixed to the VCL.

 

That'll be a laugh trying to cut they the foil but not the vcl! Going to give it a go though.

 

Conduit will enter through the hole in the bottom of the hood. It'll need a bead of something around that too.

 

 

Then all I have to consider is the losses through the conduit itself! Might gel it where it comes up into the conduit box.

 

Taking the Tesco, "every little helps" approach!

[Dudda]

2 hours ago, Onoff said:

That'll be a laugh trying to cut they the foil but not the vcl! Going to give it a go though.

Slide something thin like a piece steel or aluminium sheet, MDF or if you've a hobby cutting mat that would be ideal between the VCL and insulation. 

[Nickfromwales]

CT1 would bridge and maintain the vcl.   

[Onoff]

 

2 hours ago, Nickfromwales said:

CT1 would bridge and maintain the vcl.   

 

Probably but I was aiming for something intumescent. I have a few tubes of this I was hoping to use:

 

 

Says it's "tested for air permeability to EN13141-1" whether that has any bearing...

 

Edited January 20, 2018 by Onoff

[Nickfromwales]

Bingo. 

But available from the CT1 family too. 

http://www.wilsonspaints.co.uk/product/c-tec-ct1-fsb-fire-seal-n-bond/

[Onoff]

23 minutes ago, Nickfromwales said:

Bingo. 

But available from the CT1 family too. 

http://www.wilsonspaints.co.uk/product/c-tec-ct1-fsb-fire-seal-n-bond/

 

'Kin how much???

[PeterW]

52 minutes ago, Onoff said:

Probably but I was aiming for something intumescent.

 

Why...?

 

If you use a Fire Rated downlighter then it will include a fireseal. That is enough to make the seal work, and unless you use a full set of 60 min intumescent products to form a full fire system then there is always a weak link. None of this is relevant for that room....

[Nickfromwales]

The body drier will be a bigger fire bridge. 

[Onoff]

6 hours ago, Nickfromwales said:

The body drier will be a bigger fire bridge. 

 

 

For that I'm thinking a big box made from pink plasterboard. Then with the vcl over that.

[Onoff]

These cry out to be foamed in imho (not trimmed the foil/vcl yet and not the final cabling which will be in 20mm galv):

 

 

 

[CC45]

Pretty neat work there.

[Onoff]

So I knocked up a template. Drew round the Thermahood with a Sharpie on some scrap ali then cut out the exact shape with some tin snips:

 

 

With my home brew Starrett adapter...

 

 

I can attach the hole saw I used...

 

 

This is the gist but the Stanley type knife, even this small one, is too big to wield and cut around the corners, off to find the scalpels! 

 

 

And YES that is a faux pas with a hole in the wrong place!  My only excuse is that I'd had a 600ml bottle of Cobra and the mark where to drill was one of 3 discussed with SWMBO

Edited January 24, 2018 by Onoff

[Onoff]

What I was aiming at:

 

 

 

[DundeeDancer]

I went for the following in the kitchen area instead of down lighters:-

https://www.amazon.co.uk/gp/product/B01FDKG636/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Surface mounted and quite small.

[Nickfromwales]

44 minutes ago, DundeeDancer said:

I went for the following in the kitchen area instead of down lighters:-

https://www.amazon.co.uk/gp/product/B01FDKG636/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Surface mounted and quite small.

I use the recessed ones these days. They're only the thickness of the plasterboard + matchbox sized tranny, and the dispersion compared to spotlights is 10-fold better. 

[PeterW]

19 minutes ago, Nickfromwales said:

I use the recessed ones these days. They're only the thickness of the plasterboard + matchbox sized tranny, and the dispersion compared to spotlights is 10-fold better. 

 

Shame you can’t get them in Part E / Fire Spec as they would be great if you could. 

[Onoff]

I considered the thin ones but would have had to puncture the vcl anyway. A case too go with what you like and I like Aurora! Any I wanted to see "if I could" with the whole Thermahood thing.

 

Let's face it this ceiling didn't really need a vcl...I should have looked to have the loft space above inside the warm envelope. Spilt milk etc!

[Carrerahill]

On 18/01/2018 at 20:34, Onoff said:

Just about to puncture in earnest my lovely plasterboard ceiling for 5(6) downlights and in particular the continuous vcl that sits above the moisture resistant plasterboard.

 

I've had it planned to do like this for a while but will my idea to maintain the airtight layer work? 

 

So, between the joists its fully filled with 100 + 50mm of foil faced PIR. I'm using TH140 Thermahood downlight covers that measure 185 x 185. A rigid plastic type they are. They have no bottom flange really as per the sketch (the circular ones do but I like squares). So I drill up from below my 60mm dia hole that goes through the plasterboard, vcl and into the foil faced PIR a bit. Then with a long series pop a hole up through the PIR. Into the loft with my 200x200 wooden jig, centre over the hole and neatly cut out the PIR. At this point I have the opportunity to LEAVE the bottom layer of foil intact as the PIR just peels away. That is above the vcl. Ideally though I want the vcl outside the 185x185. So I cut back an exact 185x185 section of foil and vcl and centre the Thermahood over the cut out. I figure just a bead of intumescent sealant around all 4 sides should do the trick or should I invest in some airtight tape? To maintain the insulation I'll be adding a 150mm deep slab over the hole area above the downlight. Plenty of height to do so in what is dead space. There's a good 300mm between the tops of these ceiling joists and the underside of the dormer extension floor joists.

 

Do I need to fill the void outside the tapered sides of the Thermahood? Low expansion foam maybe? Or can I leave this void unfilled? Thinking condensation maybe? Cheers.

 

 

I would be installing a good quality fireproof sealed (IP65 or better) LED down-lights in this space. The bezel on good ones comes with a seal to but this can be made.

 

If you use the right product then it will have all the properties you need.

 

Decent quality commercial grade down-lights would be the best option - if money is of consideration then something like this would work: https://www.screwfix.com/p/luceco-f-type-fixed-fire-rated-led-downlight-white-800lm-8w-220-240v/9966T?tc=IB4&ds_kid=92700030354322698&ds_rl=1245250&ds_rl=1248181&ds_rl=1249484&gclid=EAIaIQobChMIxbuQp_PD2QIVbr7tCh1CIQgqEAQYAyABEgLjuvD_BwE&gclsrc=aw.ds&dclid=CKHLpqjzw9kCFTED0wodDYcKPA

 

Note you can get 2 of these in Costco at the moment for £22.

 

These can also be covered with insulation - good quality LED fittings will under-run a better chip which means heat is less of an issue - which is why insulation coverable fittings are now much more common. 

 

 

Edited February 26, 2018 by Carrerahill

[Onoff]

@Carrerahill, cheers for that but I've got all bases covered. I paid  £12 ea for these:

 

https://www.ledbulbs.co.uk/enlite-e8-8w-fixed-dimmable-fire-rated-led-downlight-cool-white

 

So IP65, fire rated & with a seal. 

 

But...the seal on these (or any other downlights) is no way as good as the vcl I've punctured to fit them. I'm trying to create a cavity whereby the vcl is reinstated as best as I can. The vcl will be the Thermahood.

 

[Roger440]

5 hours ago, Onoff said:

@Carrerahill, cheers for that but I've got all bases covered. I paid  £12 ea for these:

 

https://www.ledbulbs.co.uk/enlite-e8-8w-fixed-dimmable-fire-rated-led-downlight-cool-white

 

So IP65, fire rated & with a seal. 

 

But...the seal on these (or any other downlights) is no way as good as the vcl I've punctured to fit them. I'm trying to create a cavity whereby the vcl is reinstated as best as I can. The vcl will be the Thermahood.

 

 

As i spent the weekend trying to sort out downlights (not fire rated in the downstairs kitchen signed off by the BCO!) im struggling to understand why you didn't just use the downlight you have (the enlite one). Why the hood, sealant etc, as the downlight meets the regs does it not. Is it just SOLELY for the reasons stated i your last sentence? 

 

 

[Onoff]

Just now, Roger440 said:

 

As i spent the weekend trying to sort out downlights (not fire rated in the downstairs kitchen signed off by the BCO!) im struggling to understand why you didn't just use the downlight you have (the enlite one). Why the hood, sealant etc, as the downlight meets the regs does it not. Is it just SOLELY for the reasons stated i your last sentence? 

 

 

 

Regs are often a poor minimum imo.

 

Just to try and reinstate a continuous vcl.  I am absolutely sold on the whole vcl / draught proofing idea. Makes SO much difference.