Beam/block Vs. Solid Vs. Suspended Timber floor for extn

[MAJ786]

I'm not a builder / technician, but I am a bit techy.

I'm getting to floor stage on an 12 sq. m extension to a 17sq m kitchen (ground floor). We want to put in underfloor heating in the new larger floorspace - water circuit, not electric.

The house is a 1960's detached. existing floor in the kitchen appears to be suspended timber (tiled at the moment), though a neighbouring porch seems to be solid/concrete.

My Building Regs Spec currently says 150mm Hardcore+25mm sand binding + 1200gg DPM +150 conrete slab + 75mm Celotex+75mm sand & cement.

My Structural engineer friend had recommended Beam and Block - which I guess is "solid suspended".

My builder wants to use suspended timber: He justifies this by saying that it will be better from a materials point of view - laying the underfloor heating will need specific materials - and they differ on solid vs.. suspended wood floor.

Is my builder right. He seems to know what he is doing.

 

[dann09]

Solid floors and beam and block came in because of costs ref. suspended timber floors.

IMHO, suspended is a far better floor esp. in an extension where it will continue to provide through ventilation ( without any finicky detailing ). And for a number of other advantages.

However, materials will cost more.

If you go suspended, then have a sectional drawing knocked up to be certain of FFL esp. with UF heating in-situ.

 

[RonnyRaygun]

Is there a reason you can't have a ground bearing slab? It's usually the most cost effective option. You've just got to ensure the airflow to the suspended floor is maintained.

With ground bearing slab or beam and block, the UFH pipes will be laid in the screed above the insulation.
With timber, it's not as simple. There are aluminium plates that can be used to route the pipes below the floorboards. Some argue that the UFH is less efficient in timber floors as the floorboards are a better insulator than screed.

Maybe talk to a UFH expert for their opinion.

 

[freddiemercurystwin]

as mentioned you would only do suspended if you need to continue the ventilation of the existing house floor void or if your floor level is much higher than the existing ground level. In anycase either B/B or ground bearing concrete will be best for UFH.

This thread may be useful //www.diynot.com/forums/building/sub-floor-on-extension-concrete-or-floorboards.345111/#2581609

 

[MAJ786]

The floor is reasonably high above the ground level (35/40cm).

There are two existing vent bricks that would need "feeding" from new ones in the new exterior wall. In fact one surveyor suggested a third vent would be needed, pre-extension (when I bought the place in '97).

My builder is suggesting, "bekka boards" throughout for better efficiency.

 

[dann09]

Just re-read your OP and the suggestions from others.

1. your existing kit. is a suspended floor?

2. Is the concrete porch included in the extn. floor plan?

3. I didn't realise that you wanted a hydro system. I prefer electric, i think it's cheaper and has less to go wrong, but experts will know best for your situation.

4. If a surveyor has already indicated a lack of thro-ventilation, then thro-ventilation must be taken into account in your decision.

5. With the oversite crawlspace height, if you do go suspended then be sure to clear the o/site and leave an access through the main(kitchen) wall.

6. If you go solid floor then a new section drawing is req'd for the hydro installation.

 

[MAJ786]

2. Is the concrete porch included in the extn. floor plan?

No.

The porch is separate and already has electric UF heating under tiles.

 

[^woody^]

If you want a bouncy floor that rattles the crocks in the cupboards as you walk across it, then go for suspended

The only advantage in beam and block its for the builder on terms of speed of construction.

Also, despite insulation, the air void means that you lose the benefit of heat and mass from the ground - which is even more pertinent as you are planning to instal underfloor heating.

 

[MAJ786]

Builder has also warned that retro-fit of UFH will raise the (existing) FFL slightly compared with hallway (also suspended timber, but carpeted), but that he will do what he can to minimise it.

 

[dann09]

"if you want a bouncy floor" - not necessarily so. Joistings well dried and wedged in with slate and plastic wedges will hold well in a typical extn. span. Screwing and gluing the T&G chipboards/ply will further tighten the floor.

We constantly replace long joist spans in damp and timber situations, and the only call-backs that i recall have been due to softwood wedges shrinking.

 

[freddiemercurystwin]

If you want a bouncy floor that rattles the crocks in the cupboards as you walk across it, then go for suspended

The only advantage in beam and block its for the builder on terms of speed of construction.

Also, despite insulation, the air void means that you lose the benefit of heat and mass from the ground - which is even more pertinent as you are planning to instal underfloor heating.

Maintaining the ventilation to the void under the existing is much easier, otherwise he's faffing about with pipes etc. Anyway the OP seems set on timber suspended no matter what and if so then the OP should consider over-specing the joists not holding back on noggins etc and ensuring the lot is as tight as a Nats chuff or it will bounce. You can get bounce with B/B too.

What are bekka boards or am I about to embarrass myself again?

 

[freddiemercurystwin]

chipboards.

Never for a kitchen, elsewhere OK but not for a kitchen.

 

[theoldun]

Would suggest that you read the thread that Freddy has posted. Will answer most of your questions and give you approx costings..
Will just add this, in our opinion electric UFH is not worth a candle, especially on timber suspended floors. Even the electric UFH bods admit that it is no where efficient as wet UFH, plus the costs mount up and up with installation on suspended timber floors. If we have a small extension, we may throw a solid slab in, but from anything 16ms and up we go block and beam, as it is so much easier, quicker and efficient..
With regard to heat loss through the under floor void, this is taken into consideration on the Perimeter/Area ratio in Technical Note 10
The rules for air bricks are 450mm in from each end and 2m or there abouts centres.
QUOTE. builder is suggesting, "bekka boards" throughout for better efficiency.
Have you spelt that right, as have never heard of them.
Regards oldun

 

[dann09]

Suggest, perhaps "backer boards"?

 

[MAJ786]

"bekka boards" throughout for better efficiency.
Have you spelt that right, as have never heard of them.
Regards oldun

looks like this is what he means: BEKA foli-mat

http://www.beka-klima.de/en/thin-layer-underfloor-heating.html

To be fair I just spoke to him again, and he says he does not mind going Beam and block, but there will be more work as to match the existing floor level he'll need to drill out some concrete that is in place in the, erm, I guess it's termed "oversight" (the new extention floor ground level).