I have recently watched a few videos of extensions being built and noticed that in common with new builds ground floors are now solid concrete. However on one such build block and beam was used with no explanation why?
What would be the reason to favour block and beam over solid concrete, or is that too going the way of suspended wooden floors? In all cases extensive insulation was used either under the concrete or on top of the block & beam and UFH used.
Speed ... the beams can be hoisted into place and blocks dropped in between, they can immediately be walked on, have piles of brick/block stored on top to continue building the walls ... a fairly sloppy slurry/grout needs to be brushed into the joints at some stage.
I was recommended to use block and beam because my floors were very big and the soil was wet clay with tree roots in it.
The explanation given was that the soil would in time dry out and shrink and crack any concrete floor laid on it: an air gap under the blocks and beams allowed for this.,
So I had various internal foundations put in going down quite far to rest the beams on.
It worked out well.
Whilst that is to an extent true, it's not the general reason. Large concrete slabs laid on the ground will in time crack and sink due to soil drying out beneath them and the thickness and amount of rebar needed to stop this makes the whole thing more expensive than block and beam, whereas for a small extension, a thinner poured slab is OK.
+1 for the conservatory we had built. It was also considerably cheaper to use block and beam than solid concrete.
I didn't think it was that economical unless you purchase a lot of beams, as they need to be made to your dimensions.
According to the structural engineer 10 years ago: "I think the answer to this is 1.5m deep trench fill footing (+ clayboard and beam and block floor) this has to be the cheapest and best solution. To build a raft you have to dig out to 750mm + an extra 1m to perimeter of conservatory and backfill with crushed rock (type 1) and build a 250mm rc raft on top of that."
Some that I have kicking around, have their length scrawled into the wet concrete on the bottom, but I'd have thought it was equally possible they make various stock lengths, and just use a sawto chop a few inches off to make your size?
From memory all the strength is in the beams - the blocks are pretty weak and easily cut
Correct. From memory, around ten 4m beams were required. Most of these were used full length, but the conservatory had a 2m x 2m bridge from the patio doors to the main 4m x 4m section (to avoid building over the sewer access). The beams for the 2m bridge were made from the 4m beams with a cutting disk.
Yes, I was talking about the beams, you can see where the reinforcing wire was cut at the ends
I much prefer suspended floors - it gives simple routes and access to add/change plumbing and wiring in the future, without having to get everything down the walls from the floor above.
That may be true of wood, but it aint true of block and beam
No way you can punch through that to add pipes. or wires
ALL my services come down from above: Nothing is routed underfloor except vents for combustion devices.
I walked past a new build development in Coalville (Leics) in January that was just out of the ground and the block and beam floors had just been installed. Coal mining country but the street is otherwise full of 100+ year-old terraced houses. https://www.google.co.uk/maps/@52.7175935,-1.3764528,3a,75y,141.87h,84.33t/data=!3m6!1e1!3m4!1skCYlirr1p97mZQm2d5oR4g!2e0!7i16384!8i8192?hl=en&entry=ttu
Our house is block and beam on two of three floors (it is split level). On those floors, there are significant gaps to ground level.
When a new house was built next door, the ground floor was also made of block and beam. At the rear, due to the slope of the land, there is probably room for a basement to be added.
Beware the camber! Our 4.5m x 8.5m balcony was done in block and beams.
There is a very significant camber can't remember exactly but it's in excess of 10mm fall awy from centre to end of beams. This also has the problem of adding a bit of deflection to the surface if you step quite heavilly in the centre so if insulating on top of the block @ beam you'd still need to screed over the top before laying the insulation.
In 2021 my wife and I purchased a 50 year old bungalow in poor condition. It was built on a slope.The front has timber floors, the rear half, all concrete. A garage at the side was too dilapidated to be used for anything.
We had it razed and an extension built in its place. The builder asked me do you want a timber or concrete floor?
The timber floors contribute to draughts so I chose concrete.
When construction got to the point of starting the floor I was amazed that they were using block and beam. I didn't ask any questions. After laying a liner they laid 100mm of Celotex both on the floor and in the ceiling and something similar in the cavities of the three outside walls. They added another liner followed by a cement screed.
Now that I am using it, the heat loss is palpably minimal.
Good luck with your choice.
Alan
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.