Adding a floor to upper level: joist centres 43inches apart

[BrianEl75]

I live in an older house (1841) where the upstairs level currently has no floors. The ceilings in the lower habitable level rest on top of the support beams/joists.

My ultimate goal is to convert the upstairs level so that it is habitable, but realistically this will be a multi-year project.

The upstairs level is 150m2 (roughly 12.0*12.5), has windows and a large (insulated) vaulted roof above where the ceiling would go (although I don't plan on adding a ceiling despite the additional volume that will require heating).

The support beams/joists that carry the ceiling for the lower level are of two different sizes and spacings (all units in inches)
1) 4.5*8.5 with 30.5 inch spacings between centres
2) 7.5*9.5 with 43 inch spacings between centres

When we bought the house the structural engineer said that these beams wood support a concrete floor.

I would like to lay boarding over the ceilings, with 50mm insulation over this. Then add UFH on top of the insulation followed by a concrete screed.

At this stage I am only concerned with laying the boards and installing the insulation.

Given the large spacings between the beams what size (thickness) do I need for the floorboards - my concern is that they might sag when the concrete screed is laid? Can I use chipboard?

Should I add a layer (e.g. thin acoustic layer) between the floorboards and the existing ceiling or is this not required?

Anything else I should be considering at this stage (other than layout for plumbing and wiring)?

Thanks
Brian

 

[noseall]

Those beams seem pretty hefty so would it not be plausible to fix some smaller section joists between and at 90 degrees to the beams?

Or just halve the gap and slot additional joists in parallel?

 

[BrianEl75]

Thanks, smaller joists at right angles would definitely be a solution.
If there is any possibility of laying boarding directly (presumably cheaper and also less effort) that would be my preference.

 

[Deluks]

Over 30 and 43 inches, any standard timber floor covering would sag and bounce. You'll need very thick boards, especially if you intend to screed. Maybe a precast concrete slab floor, or a roomfull of acros and poured reinforced slab.
I know what would be cheapest though, and its already been suggested.
Why do you need 50mm insulation between levels? 10mm warm-up boards would suffice here.

Are you wanting the beams to be visible from the room beneath?

 

[catlad]

You should seriously look at countering with say 3x2 as you will need it to level the floor out, and you must have the room if you are going for the vaulted ceiling. I don't understand insulating between floors.

 

[mointainwalker]

I have UFH installed on an upper floor: felt it was pointless to insulate as any heat passed downwards stays inside the habitable space and the insulating materials are quite /very expensive depending on choice.

 

[BrianEl75]

Thank you all very much for your replies. They have given me a lot to think about. I have done a fair amount of DIY over the years (plumbing, wiring, tiling etc) but have never undertaken what I would consider to be a building project ... hence probably a number of stupid questions.

To answer the questions on the insulation for the UFH ... I had assumed I would need this, but if not so much the better. The house is already quite large (there are two existing levels of 150m2) making me quite conscious of heating bills and insulation.

After some thought Noseall’s original suggestion of right angled joists seems to be the most sensible solution and I think that is what I will go with. Any recommendations for the size of joist I should go with and the spacing and the thickness of boards required to cover them?

I am also reconsidering the concrete screed and thinking of simply have a suspended wooden floor. Will the UFH still work well enough? (I am not entirely sure how high the roof is – difficult to measure in the absence of a floor - but I estimate that the total volume of upper level + roof space is 700-800m3).

One of my concerns is the sound insulation between levels (tv, music etc). Any suggestions on how a good level can be achieved?

Deluks, the beams are visible from below. I have attached a photo of each of the different beams. The ceiling above the pine beams is 14mm tongue and grooved pine. The ceiling above the larger beams seems to be bespoke. It consists of (35mm) wood strips with plaster in between. The panels have steel frames.

Catlad, to make sure that I have understood correctly, when you say “countering with say 3x2” do you mean 90degree 3x2 joists on top of the existing beams? Floor height is not an issue as the existing wall height is approximately 3.2m (although the bottoms of the roof beams are about 50cm lower than this. The roof is a pyramid shape with a slope of about 45 degrees. Picture attached.

Untitled

• BrianEl75
• 26 Dec 2012
• 1

Untitled

• BrianEl75
• 26 Dec 2012
• 1

Untitled

• BrianEl75
• 26 Dec 2012
• 1

 

[mointainwalker]

I am also reconsidering the concrete screed and thinking of simply have a suspended wooden floor. Will the UFH still work well enough?

Much worse. Whether good enough, who knows ? Perversely, if you were to do that, I think you would need to re-instate insulation as your upward heat-transfer would be significantly less and you would need to minimise losses from that space. If cost were a reason for eliminating the screed, then you have to consider buying aluminium spreader-plates ( or make your own ) which are also fairly expensive.

A screeded floor will give you much better sound-insulation

 

[catlad]

Yes as Noseall suggested 90 degrees to existing joists, if it is anything like the couple I have worked on it will help you to level the floor out.