Ground floor for bungalow: joists better than a slab?

[Dreadnaught]

I am choosing my timber frame company for my modern bungalow in Cambridge.

 

One respected company has offered a floor made of eco-joists rather than the usual reinforced concrete passive slab I had assumed. I am worried about the floor sounding hollow and making the whole dwelling feel flimsy and insubstantial: 

1. Anybody have experience of a ground floor made with joists?
2. Could I perhaps screed such a floor to give it a more solid feeling (and create a space for UFH)?
3. I wonder if such a construction would be cheaper than a passive slab. Any guesses?
4. Any other pros or cons to using joists for ground floor?

Overall what do people think, joists or slab?

 

(My foundation system is screw piles. The build will be near passive.)

(By the way, with joists I know I would lose the ability to use a slab as a thermal store).

[PeterW]

How are they planning to insulate under the floor ..?

 

If they are  planning to build some sort of cassette type floor it will be very rigid however you need to understand the edge detail as it will be above the ground and you need to stop stuff getting underneath. 

[Dreadnaught]

3 minutes ago, PeterW said:

How are they planning to insulate under the floor ..?

 

This company is a specialist Passivehaus provider. I haven't got all the details but I assume the floor would be insulated like a wall, 300 mm or so of blown cellulose insulation between the joists.

[MikeGrahamT21]

Go with concrete every time i'd say. I have timber joists in ground floor, and though i'm very thankful with it being 1960's, that i don't have to dig up old concrete to insulate it, you always have thermal bridging with timber, which you wouldn't with concrete, plus the thermal store as you've said. With timber there is also the element of ventilation to consider, which you wouldn't with concrete, and depending on what timber they use for it, the chance of insect attack, woodworm is horrible!

[Gone West]

It seems to me there could be more potential problems with a metal web joist ground floor than concrete. So I would use concrete.

[redtop]

must be millions of Victorian homes still standing with suspended ground floors and nothing but mud underneath.  Bloody cold though ? still I think its probably easier with concrete (and certainly nothing to go wrong once done) but perfectly possible with joists, insulate between is easy; could wrap external cladding below that to remove cold bridging if room allows

[PeterW]

3 minutes ago, Dreadnaught said:

 

This company is a specialist Passivehaus provider. I haven't got all the details but I assume the floor would be insulated like a wall, 300 mm or so of blown cellulose insulation between the joists.

Sounds ok but would still want to see the edge detail - fully filled Cellulose will sound solid but I would want joists at 400 centres for rigidity. 

[Patrick]

+1 on all the others. I was thinking long and thoroughly about timber ground floor as I have a issue with access and anything lightweight is a massive bonus. But it's just too much of a risk. I understand that 1000s of victorian houses have suspended timber floors which lasted centuries and that with treated Web joists or ibeams, they should be fine for moisture, but with concrete you get a tested system.

There is a reason why most (not all) foundations are build from concrete nowadays. It's quick, easy, solid and cheap. If you have decent access there  really isn't any benefits of suspended timber ground floors. It's not much cheaper and by the time you make it work (e. G. What you say, put a screed on top) like a concrete floor, you probably level with costs, and apart from price there really isn't any great benefit in timber ground floors.

[willbish]

With joists you'll have a greater delta T to contend with.

Air temperature being a lot colder than ground temperature in the winter.

So you may need more insulation if using joists for same performance.

[joe90]

+1 for concrete fir all the above reasons and get your UFH pipes in it, job done.

[Dreadnaught]

Thanks all! Good advice.

 

Just spoke to the MD of a different timber-frame company this morning. When I mentioned this choice he also said emphatically to choose the concrete slab every time as it gives a much better result and he said it won't cost much more. And his company offers joist-floor solution! 

 

I will be visiting him next week and he said he has test-built examples at his factory of houses using both floor types to show me.

Edited November 18, 2019 by Dreadnaught

[Thedreamer]

1 minute ago, Dreadnaught said:

Thanks all! Good advice.

 

Just spoke to the MD of a different time-frame company this morning. When I mentioned this choice he also said emphatically to choose the concrete slab every time as it gives a much better result and he said it won't cost much more. And his company offers joist-floor solution! 

 

I will be visiting him next week and he said he has test-built examples at his factory of houses using both floor types to show me.

 

A lot more work in insulation, ventilation etc.

 

I think these days people only ever go with a suspended timber floor if there is a good reason for this. For us this was due to ground conditions and a sloping site.

[colin7777]

How does Concrete slab compare to Beam and Block on cost, weight and insulation.

 

We have a ground floor area 12 metres by 6 metres, it needs to be on piles with a steel ringbeam as water has to be able to flow through in a flood situation. The gap from soil level to ground floor level will be approximately 500 mm, so looking for best solution

 

Thanks

 

Colin

[PeterW]

@colin7777 Considered concrete planks ..?? 6m is a small span for these and you could build yourself a working platform in less than a day with these craned in and then you can go straight off the top of that. Stronger than beam and block and potentially less of a flood issue. 

[epsilonGreedy]

4 hours ago, redtop said:

must be millions of Victorian homes still standing with suspended ground floors and nothing but mud underneath.

 

 

The Victorians used up the last of the decent land with a bit of natural drainage in the east of England, we 21st century builders in Cambridgeshire and Lincolnshire have to contend with more ground moisture.

[joe90]

21 minutes ago, epsilonGreedy said:

we 21st century builders in Cambridgeshire and Lincolnshire have to contend with more ground moisture.

 

Do you mean flood planes? ?

[Onoff]

6 minutes ago, joe90 said:

flood planes

 

Like at Chennai airport?

 

[epsilonGreedy]

10 minutes ago, joe90 said:

Do you mean flood planes? ?

 

 

Floodplains would be included though my plot is not in a floodplain which I think of as being specific to a river valley. Other local peculiarities can create a boggy plot that prior generations of house builders avoided.

 

I forgot to include the Somerset Levels in my regional assessment, welcome to the boggy plot club.

Edited November 18, 2019 by epsilonGreedy

[joe90]

27 minutes ago, epsilonGreedy said:

welcome to the boggy plot club.

 

I think I am definitely a member, ask @SteamyTea what our ground is like!, 10inches of suspect soil on solid yellow clay, either very boggy or hard as nails and cracked in dry weather. Despite being like this we never flood as there are no rivers near us.

[SteamyTea]

34 minutes ago, joe90 said:

either very boggy or hard as nails

Get those willows, poplars, eucalyptus and Leylandii planted.

[joe90]

59 minutes ago, SteamyTea said:

Get those willows, poplars, eucalyptus and Leylandii planted.

 

Not leylandi ,!!, have planted 50 poplars

[SteamyTea]

4 minutes ago, joe90 said:

Not leylandi

I think they would be a relatively quick way of drying up, and breaking up, some boggy land.  Would need to be chopped down after about 5 years or so, then more interesting things done.

[Simplysimon]

46 minutes ago, SteamyTea said:

I think they would be a relatively quick way of drying up, and breaking up, some boggy land.  Would need to be chopped down after about 5 years or so, then more interesting things done.

if you chop them down it'll only get boggy again, would break up the soil though. heard yesterday on gqt about a guy planting sugar beet on his ground, waited until roots had gone deep and broke the soil down and dug it all in to improve the quality.

[SteamyTea]

3 minutes ago, Simplysimon said:

planting sugar beet on his ground, waited until roots had gone deep and broke the soil down and dug it all in to improve the quality.

Heard that too, and remember some old cottage gardener saying he used potatoes to break up his soil.

 

[Big Jimbo]

I have only just picked up on this thread, so apols if i am being a plank. The OP said he was having screw piles. How does a passive slab like Harris and Stark have work with screw piles, or any sort of piles in that instance. I thought that the whole idea of piles was that the load being put on top, had to be spread. Ie: The piles are joined by being linked using a number of methods, for instance, concrete ring beam, steels etc ......How does a passive slab, eps, bit of metal and 4" on concrete link to the piles ??? I thought that with piles, you had to have some form of suspended floor, such as timber, block and beam, metal I beams etc. The whole idea is that the structure, walls, roof, floor, all have to bear on the piles.  Please enlighten me, I'm not being a pain, i just dont get it.......