Floor structure: thinnest with MVHR

[Sjk]

Hi,

 

Sorry another question!

 

Its a self build, aprx 5mx9m with three floors and hopefully a basement. It will have MHV and UFH.

 

Some people have recommended concrete floors throughout, I like the idea of concrete floors although I do also like the way a wooden floor 'gives' a little when you step on it.

 

Id also like to keep the floor depth to a minimal if I can, not sure if there is better type I havent considered? Any input would be greatly appreciated 

Edited October 6, 2018 by Sjk

[Mr Punter]

If you want really want concrete you will probably need to do beam and block or poured concrete as the hollowcore plank firms will not be interested in small footprint.  Concrete will be more expensive and require more lifting equipment than timber.  By the time you have space for services, finishes and ceiling it will probably be deeper than a timber floor.

 

I would recommend an Easi-Joist type engineered metal webbed floor with 22mm Egger Protect chipboard.  Specify that the maximum deflection must not exceed 8mm or 0.002 x span.  You will more easily be able to incorporate services, including your MVHR, and ceilings are easy to fit.  The floor supplier should be able to produce the design for you.

[Sjk]

Thanks Mr Punter, Ill have a look into it.

[Sjk]

The easi joist type seems to be the most suitable, do they allow for a small depth floor? My architect has allowed for the floor to be 45cm thick, it would be great to be able to get this down if possible.

[Jeremy Harris]

The floor depth depends almost entirely on the maximum span of the joists and the distance between their centres.  For example, we have a maximum span of around 4.5m, with 253mm deep Posijoists at 400mm centres.  If you have a greater single span then you'll probably need deeper Posijoists.  450mm seems very deep to me, and implies that you have a pretty long span to cover.  Worth checking the joist spacing, too, as if this 450mm depth is at 600mm centres you can probably reduce the depth of the joists by going to 400mm centres.

[Temp]

Do you have to run MVHR pipes horizontally in the floor? Could you run the pipes vertically in a corner? They are likely to have to go vertically as well anyway. 

 

 

[Mr Punter]

Even with no internal walls, with a building 5m x 9m internally, 300mm deep joists will normally be fine. Allow another 60mm for floor deck, finishes and ceilings, so 360mm max for floor zones.  You can find a calculator at https://www.jamesjones.co.uk/interactive-span-table

 

The Easi Joist values are very similar.

[Gone West]

15 hours ago, JSHarris said:

The floor depth depends almost entirely on the maximum span of the joists and the distance between their centres.  For example, we have a maximum span of around 4.5m, with 253mm deep Posijoists at 400mm centres.  If you have a greater single span then you'll probably need deeper Posijoists.

An alternative to reducing centres or increasing depth is to increase the chord width of the metal web joist. Our maximum span is 5.9m at 254mm depth with 400mm centres but much wider chords.

[Sjk]

Thanks guys such great help!

 

The span should be 5m.

 

 

Found this

 

https://www.wolfsystem.co.uk/media/114954/easi-joist-tech-guide-v8-6th-edition.pdf

Edited October 7, 2018 by Sjk