Building ceiling box for fan and spotlight

[Derbyboy]

I have a ceiling fan Thermex Newcastle 90. Unfortunately, I can't embed it fully into the ceiling as I can only raise the fan 8-12 cm before the ceiling insulation becomes too much. I have a flat roof on the house.

I need to build a box for the fan. I will run it with a carbon filter as I don't want to make a hole in the ceiling.

What material should I use to build the box?

The fan will blow the extracted air into the box and I understand that MDF is very moisture sensitive. What happens to the box during something like a long simmer?

 

[JKrister]

Depends a bit on size and placement. I think the easiest would be to secure some 45x70 in the joists and let them extend down as much as needed. These posts are covered with sparse wood or plywood, which are then covered with drywall.

We built a somewhat substantial drop ceiling for a ceiling fan with a wave shape and LED strips.

 

[Derbyboy]

That was quite a project

 

[JKrister]

That was quite a project

No kidding. I think I spent 600 hours on that client.
I still believe the construction method is simple and adaptable to size.

I would discuss here or with a designer about the possibilities of not lowering it. I think it looks much nicer.

 

[Derbyboy]

Of course, the best would have been not to lower it. But I have a flat roof with:

gypsum 13mm
Råspont 20mm
Rafter 200mm
Air gap 50mm
Råspont 22mm
Roofing felt

my roof fan has a build height of 192mm so I don't have much choice. Considering recessing the box 70-80mm but that means 30-40mm less insulation right there.

I'll probably use a carbon filter on it. Not too keen on making a hole in the roof.

 

[JKrister]

Truss cc1200 with floor joists between cc600?
How big is the fan 500x600?

Went a bit fast. So you have a total of 200mm insulation, and that's where the problem lies. Not that beams are in the way?

Sorry for going off-topic but 200mm truss on a flat roof sounds a bit odd. Should be more robust.

 

[Derbyboy]

The rafters are unfortunately a bit varied, like cc80-cc110. The floor is cc60.

The fan is a Thermex Newcastle 90, dimensions about 50-60x90cm.

 

[Derbyboy]

No, the beams are positioned perfectly over the kitchen island. It's precisely the thickness of the ceiling that is the problem.