led downlights into pir insulation.

[carlos21]

i want to fit led downlights into a dormer bedroom ceiling. there will be pir insulation between the rafters and insulated plasterboard on top.

i dont really want to cut a hole through all the insulation but iam unsure how much air gap is needed around the light unit.

would surface mounted units be better?

any thoughts?

thanks carl

[JohnMo]

I found the driver for the led lights was the biggest thing. We did a 50mm service void in all ceilings. It's not just the light fittings it's also cables and driver. Also led lights need a good place to dump the little heat they make, so would suspect installing in insulation will result in a short life of the light.

[FuerteStu]

Would the low profile ones be suitable in this scenario? 

 

I've seen some almost as thin as plasterboard. 

[Super_Paulie]

i was in the same boat when the missus decided last minute she didnt want surface mounted spots on the vaulted ceiling. I found some very thin lights from Alusso. Yeah, usual stuff you expect from the likes of Amazon but they are really slim. I actually prefer them much more than my "more legit" Tapo bulbs as when they change colour they fade between them, the Tapo GU10s just go hard from one colour to the next, less impressive. I battened out 50mm over my joists/insulation and also removed a small section of it behind each light just to give it a bit more breathing room, then used a light-box from Wago to make the connections. Probably overkill as these are always stone cold.

 

Alusso

Anyways, i use the RGB bluetooth version which are more like 30mm but you can get standard white ones that are like 19mm. I bought a ton of spares for when the company inevitably go under.

 

 

Edited January 8 by Super_Paulie

[carlos21]

thanks for the replies, i had been looking into slim surface mounted units, so this may work or i might build a sort of back box out of pir, for behind the downlight.

i took one out in another part of the house and despite being led i was surprised at how much heat it generated.

thanks again carl

[Onoff]

As above why not cross batten the ceiling with 50mm timbers to form a service cavity and reboard. Leave some batten gaps so you can add lights later if you want.

 

That way your insulation layer remains in one piece with no penetrations. 

[carlos21]

On 11/01/2026 at 08:55, Onoff said:

As above why not cross batten the ceiling with 50mm timbers to form a service cavity and reboard. Leave some batten gaps so you can add lights later if you want.

 

That way your insulation layer remains in one piece with no penetrations. 

we are really short on head room so i wouldnt want to loose any!!, even 50mm.  

[Onoff]

How much insulation between the rafters? Thermahood do a 95mm high hood.

 

 

[Onoff]

I made myself a shed load of work by not battening. Had an airtight, VCL'd ceiling. I then punched 4 holes for down lights, 2 for Bluetooth speakers and a bfo one for a body dryer. 

 

I have a plan to reinstate the insulation and airtightness on all the penetrations. Been saying that for a few years! 😂

 

 

 

 

 

 

 

 

 

Covered with a Thermahood that I've yet to stick down and insulate around / on top. 

 

 

 

 

 

[Super_Paulie]

15 hours ago, Onoff said:

I made myself a shed load of work by not battening. Had an airtight, VCL'd ceiling. I then punched 4 holes for down lights, 2 for Bluetooth speakers and a bfo one for a body dryer. 

 

I have a plan to reinstate the insulation and airtightness on all the penetrations. Been saying that for a few years! 😂

 

 

 

 

 

 

 

 

 

Covered with a Thermahood that I've yet to stick down and insulate around / on top. 

 

 

 

 

 

 

interested in the body dryer. Any good?