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Flat duct through screed floor - not deep enough?


Conor

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My Elica hob has just arrived. The duct out kit that comes with it has 220x90mm duct. Our floor build up is 150mm precast slabs with 100mm screed (50mm TLA, 50mm liquid) and finally 18mm hardwood floor.

 

This means the duct will be within the depth of the screed floor but with only 10mm on top to the underside of the wooden floor. The duct will be installed after the screeding is finished. Can I just pour 10mm of self leveller over the duct and then lay the wooden floor? Will the PVC duct be OK?! I'm worried about the duct collapsing and floor moving. I'm thinking I might need to build some sort of ply channel to protect the duct and forgo the self leveller on top.

 

I could go down through the precast slab to the basement ceiling void but it's a nightmare of electrc cable cages and more than one MVHR duct blocking the exit route. Would mean a duct run of at least 8m which is not ideal.

Edited by Conor
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56 minutes ago, Conor said:

My Elica hob has just arrived. The duct out kit that comes with it has 220x90mm duct. Our floor build up is 150mm precast slabs with 100mm screed (50mm TLA, 50mm liquid) and finally 18mm hardwood floor.

 

This means the duct will be within the depth of the screed floor but with only 10mm on top to the underside of the wooden floor. The duct will be installed after the screeding is finished. Can I just pour 10mm of self leveller over the duct and then lay the wooden floor? Will the PVC duct be OK?! I'm worried about the duct collapsing and floor moving. I'm thinking I might need to build some sort of ply channel to protect the duct and forgo the self leveller on top.

 

I could go down through the precast slab to the basement ceiling void but it's a nightmare of electrc cable cages and more than one MVHR duct blocking the exit route. Would mean a duct run of at least 8m which is not ideal.

As you only have 10mm above I would not screed over the duct, the screed will crack and break up.

I would screed and allow an inch or so either side clearance, then after laying the duct, grout up to top of duct level and cap off with 10mm ply or OSB so most of the load is transferred to the grout/screed and duct verticals.

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It's a tricky one. 

 

You could substitute your 220x90 for 4x 110x54 mm ducts spaced out so the screed could bridge the gap. 

 

The most robust solution is probably down through the floor in the unlikely case you ever need to access the them again. 

 

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I'm now thinking going down through the slab is the better option, and probably less work. I can reroute the two MVHR ducts and remove a section of the electrical caging and go straight out with the ducts provided. Really dont like the idea of the duct below the screed - agree with Mark that best option would be to build over withe  bit of ply. but at that, 10mm ply isn't great.

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Assume you have a job with extractor.  To pose a different question, do you need to duct out? Could you just install a carbon filter and exit into room?

 

Not sure if you have mvhr, that would take away any steam generated

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1 hour ago, JohnMo said:

Assume you have a job with extractor.  To pose a different question, do you need to duct out? Could you just install a carbon filter and exit into room?

 

Not sure if you have mvhr, that would take away any steam generated

 

 

We bought the duct out version of the hob... I'm now rethinking that and will investigate the recirculating option. We do have an MVHR and have a double flow rate extract in the kitchen. I think I might get the kitchen finished and get MVHR up  and running before doing anything drastic like cut through floors. Wooden floor wont be going down for 2-3 months anyway. Plenty of time to see how much we need the extract.

 

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  • 1 month later...

I have a similar situation and I would like to hear other's opinion.

 

A downdraught extractor (Bosch made) to be installed in a kitchen island. The plan is to discharge extracted air to the atmosphere via air brick on the external wall face. (no MVHR)

The floor construction is/was "Beam and Block" - "100mm Celotex" - "75mm screed with UFH pipe" - "10mm floor tiles".

The exhaust duct is 220 x 90 mm PVC.

 

To achieve a more "robust" floor, I am thinking to change the floor build-up as:

  • "Beam and Block" - "110mm Celotex" - "65mm screed with UFH pipe" - "10mm floor tiles".

I will install the flat duct in the insulation layer. 100mm insulation board (cut to 400mm width) on either side of the duct. This will leave a 1020mm (width) x 20mm (deep) zone which I can use a 18mm plywood to cover / bridge. I think this arrangement should be strong but I would like to hear other's opinion or suggestions. 

 

Thank you.

 

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I would put the duct directly onto the blocks, then cover in insulation, but I would put thinner insulation to the side of the duct and bridge over the duct with a full sheet of insulation. 

Also add light weight stainless mesh to the screed over the duct area, just like you would reinforce concrete. 

 

Dont forget 10mm tiles take up far more room than 10mm when you add in adhesives and other stuff. 

 

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5 hours ago, Olf said:

Why not to discharge to the void under brick and block? Or run the ducting in the void?

 

because I don't think discharging grease air into the void is a good idea.

Ducting below the B&B would be too "low" when reaching the perimeter. Thank you

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