beam and block versus suspended timber floor

[RomanAbramovich]

i have the opportunity to choose either of the above systems for a small 1 room ground floor extension (18 sqm) - was all set to go with timber, but the bricklayer is trying to sell me beam and block. He says one of the advantages is that no oversite concrete will be required with b&b, just a ventilated air gap below, them 85mm jablite and 50mm screed on top.

both methods require air bricks - anyone have any experience of which method is more cost effective?

initially preferred timber as i can construct the floor myself with joists off masonary hangars. span is 3700mm, room width 5200mm.

 

[mointainwalker]

"..He says one of the advantages is that no oversite concrete will be required with b&b, just a ventilated air gap below, them 85mm jablite and 50mm screed on top. "

I'm a DIYer, not a builder so take that into account, but as far as the systems I know and have used, b+b needs to be covered in concrete ( 10 cm in my case) for strength as the blocks are only there to fill the gaps and are pretty weak.

This is proved, I think, by the fact that you can use polystyrene blocks for high levels of insulation instead of the normal blocks.

In short, I think your brickie is talking nonsense with his proposal and would really make me wonder about his "qualifications".

 

[Static]

mointainwalker, your refering to a composite beam and insulation block floor which consists of concrete prestressed beams, insulated epc blocks then a structural topping over..
A standard beam and block floor, is prestressed beams, concrete blocks, insulation layer and screed over.. the blocks and beams being the main structure..

Sorry RomanAbramovich but i know nothing of Russian beam and block manufacturers and local regulations to give you a good comparative..

 

[jeds]

Oversite refers to a concrete covering of the sub-floor. Not the floor surface.

Your builder is right that a beam and block floor may eliminate the need for concrete oversite - whereas one is always required beneath a timber floor. However, there are situations where concrete oversite may be needed beneath a beam and block floor as well.

My advice is check with your building inspector. He will be aware of the local conditions and will be in a better position to advise you accordingly.

You obviously also need to consider the overall cost.

 

[r896neo]

Block and beam is great for sloping sites and sites where access is good. It gives a well and easily sealed floor which timber can do but with more work.

If the beams and blocks have to be moved any distance it becomes a bit of a chore. Also i would imagine if you can do it yourself timber will be considerably cheaper.

 

[RomanAbramovich]

thanks for the advice folks, i really wanted to do away with having 100mm of oversite as the foundation crete was pumped in at considerable cost, due to tricky site access. to have mr.concrete return with pump for a poxy 1.8m cubed of oversite would make me cry!

will speak nicely to the bco, see if he'll take pity on me. the ext is over an existing patio, so there might be a chance i can get away without oversite, and go for suspended timber (50x200 @ 400 centres for 3700mm span). due to sloping site there will be a 250mm void under joists.

 

[RedHerring2]

to have mr.concrete return with pump for a poxy 1.8m cubed of oversite would make me cry!

Two guys should be able to mix on site that amount in an average day, so long as the materials are close and not much travelling with barrow is required, especially as oversite concrete doen't require much of a finished surface.

 

[RomanAbramovich]

distance from mixer to location for oversite is about 6 feet! how many bags of ballast and cement would I need to mix 1.8 cubed? or is it more economical to buy sand and gravel individually, rather than ballast?

 

[hotrod]

how many bags of ballast and cement would I need to mix 1.8 cubed?

3 grab bags of ballast and say 20 bags cement will be near as damn it - give or take a couple of cwt either way depending on how well you've done your calcs .

Stone and sand or all-in-ballast no real difference price wise. I prefer to mix my own but that's historical. For 1.8 cube I would want readymix anyways