Ground floor slab vs beam & block question

[Ruggers]

I have a query relating to using the slab method. I'm looking at the cheapest option for a detached self & to get an accurate price for both options, The ground floor total area including internal garage equals 125m2, 30m2 for the garage and 95m2 for the house. I've got a price for beams with infill blocks.

The garage will be slab floor anyway, but I'm unsure on the remaining 95m2 of the house. I've done smaller slabs before by myself, but not on the scale of a full house.

On a full house with 4 large ground floor rooms, how is the 150mm sub base put in place, along with the sand blinding and then 100mm of concrete, is a digger required to load everything in? How is the concrete put in when a pump isn't used, (No one really uses pumps locally) The additional labour or digger hire could make a slab more expensive than beam & block. As mentioned, i still need to use the slab for the garage regardless.

 

[RonnyRaygun]

Is ground beariing slab definitely ok to use?

Why do you have to do ground bearing slab for the garage?

 

[Ruggers]

Building control have approved it this way, its a small private development site and the others have used b and b. Its on a slight slope and its a fine between which is most suitable. The down hill side would need more sub base to build up to level if slab is used, the up hill side will need a little more excavation where beams would be used. I can re use the soil renoved but sub vase needs bought in.

Materials only, The beams with blocks come in around 1200 more expensive.

I could reduce labour by installing blocks once the beams are set out but im guessing for slab a lot more machinery will be required and labour?

I just thought the garage would be better load bearing as a slab plus it has to sit 150mm lower than the house so a lot of digging out. Slab does suit this area better.

 

[noseall]

Depends how big the floor beam units are and what is required to move them into place.

 

[Ruggers]

35kg/lm and the longest is 4.9m. I spoke to the builder today who said they have their own lift so the beams aren't an issue. For slab sub base I'd need a digger to load it in because there will be a lot, I worked out 40 tonne at 150mm if stone is 2 tonnes per 1m3. They never really commented on price difference for labour and said it's much a like. Thinking about it more, the beams wouldn't be weather dependant like sub floor slab.

The finished floor is going to be 50mm screed for either option. It really seems to boil down to labour vs time vs how much a digger costs out of the £1200 slab reduced price. I could load blocks in myself to beams but slab theres not as much you can do thats not getting in the way.

 

[noseall]

Thinking about it more, the beams wouldn't be weather dependant like sub floor slab.

Neither would a sub slab, particularly. As long as it it not too hat or too cold. Rain wont matter a jot, it'll only help.

 

[Notch7]

Is the builder on day rate?

otherwise wouldn’t he be giving you a price for each option?

 

[Ruggers]

Neither would a sub slab, particularly. As long as it it not too hat or too cold. Rain wont matter a jot, it'll only help.

Why is this? I thought I'd have to look for a window of dry weather to get the sub slab in and allow it to set properly.

Is the builder on day rate?

otherwise wouldn’t he be giving you a price for each option?

I'm getting a fixed price on this type of work, joiners are day rates. I just wanted to gauge how much extra work the slab would be vs the beams prior to negotiating fixed prices because I've got one or two other variables to discuss like out buildings and didn't want to over complicate things.

If the work involved is relatively similar or worlds apart then it might help me make the decision before I contact them. I'm thinking the beam install with block infill maybe 3 days, (1 day beams in, 2 days infill) The slab i was thinking a little longer.

 

[SpecialK]

Does this help make up your mind?

"Ground-bearing floors may only be used where the depth of infill is less than 600mm deep and properly compacted."

 

[noseall]

Why is this? I thought I'd have to look for a window of dry weather to get the sub slab in and allow it to set properly.

Not in the slightest. Concrete (cement cure products) love water and despise the dry or heat. Too cold (below freezing) is also harmful because the product is being denied water in another way. The only 'harmful' thing the rain will do is put a few pock marks in the tamped finish. The concrete itself will love a bit of rain. Concrete will set underwater and set rock hard.

 

[noseall]

35kg/lm and the longest is 4.9m.

That is a fair old lump of concrete. There is no fun in finessing beams that big, i.e. wiggling them about to suit the block width. I would not like to be shifting those across recently laid walls. Do your guys have a crane?

 

[Notch7]

f the work involved is relatively similar or worlds apart then it might help me make the decision before I contact them. I'm thinking the beam install with block infill maybe 3 days, (1 day beams in, 2 days infill) The slab i was thinking a little longer

There is more work laying block and beam versus concrete slab

Almost everything for a concrete slab can be done with a digger and dumper, ie: reduced dig, laying type 1, spreading sand, moving concrete - if truck can’t get close enough to run straight in from chute.

block and beam:
move each beam from where it was unloaded, usually roadside
position each beam in place
space each beam with blocks
lay blocks in and cut the last blocks as needed
cut around services where required
fit slip courses as required and infill blocks
brush in cement slurry

then later on you also have to fit telescopic vents


often block and beam needs extra sleeper walks

Im surprised concrete pumps aren’t common around your way -I would’ve thought it would be standard for a new build

 

[noseall]

There is more work laying block and beam versus concrete slab

Almost everything for a concrete slab can be done with a digger and dumper, ie: reduced dig, laying type 1, spreading sand, moving concrete - if truck can’t get close enough to run straight in from chute.

block and beam:
move each beam from where it was unloaded, usually roadside
position each beam in place
space each beam with blocks
lay blocks in and cut the last blocks as needed
cut around services where required
fit slip courses as required and infill blocks
brush in cement slurry

then later on you also have to fit telescopic vents


often block and beam needs extra sleeper walks

Im surprised concrete pumps aren’t common around your way -I would’ve thought it would be standard for a new build

In the absence of a conc' pump then B&B would just about trump it as long as the beams are wieldy.

 

[Ruggers]

Does this help make up your mind?

"Ground-bearing floors may only be used where the depth of infill is less than 600mm deep and properly compacted."

Theres one corner thats going to be close to the 600 but not over, another around 400mm. Then the opposite side of the build will be taking more soil out and using the 150mm minimum sub base.

@Notch7 Thanks for the breakdown, theres still a lot of work involved when you list it that way. Relatively simple but time consuming & heavy to move as mentioned. People do hire the mobile concrete pumps but are usually 50+ miles away, I'm sure i recall £450 hire charge a number of years ago, does that sound right? I'll make some enquiries. It's for a self build so not a development. I'm also surprised though that the ready mix factories don't have the trucks with the booms on. Are the mobile ones for liquid screed floor different than whats used for concrete?

@noseall They said they have a telehandler so it's as good as a crane in some respects. I didn't expect 35kg/lm. It does seem like equal work in some ways if you have the right equipment. I can get the truck chute right up to the front but not enough space to get around the back, plus only the front with have hard standing to take the machine so the front half of the house is fine, the back is more of an issue. screed would just flow.

 

[SpecialK]

You could always use someone like MixaMate who mix and pump at the same time - I'm not sure what their max load is? I used them but it worked out pretty pricey I think? (7.4 cube for £1200 odd)

Hiring pumps is pretty standard now, it doesn't have to be a big craned boom one .... Just a small one on the back of a truck!

I would be concerned the 4.9m beam would be bouncy...