Beam and Block For First Floor

[Sarah29]

My SE is looking to use beam and block for the upper floor of our new build. This is raising a few unknowns which I'm trying to work out what is best. The property will have MVHR ducting and also will be screeded with wet underfloor. The property certainly doesn't have too much ceiling height to play with so I'm looking to keep this B+B floor thickness to a minimum. On the MVHR front, there is 51mm semi-rigid ducting available we can use which helps out there. Realistically how much service void space needs to be left under the beams as a minimum? Is it realistic to use the void area between the beam and blocks themselves to run this thicker ducting if positioning allows?

 

I understand B+B performs well acoustically, but would I need to incorporate other measures as well....rockwool, double board which will add to the floor thickness?

 

From an insulation perspective, can I ask what have others done on this front for an upper floor B+B?

 

Are there any low profile B+B systems anyone has used?

 

Apologies if my questions are rather basic, but any pointers or ideas people have done to keep an B+B upper floor to a minimum would be appreciated. I have not had chance to use a B+B system before.

 

thanks, Sarah

[Nickfromwales]

8 minutes ago, Sarah29 said:

Is it realistic to use the void area between the beam and blocks themselves to run this thicker ducting if positioning allows?

Any lack of continuity, and "bye-bye" to the acoustic qualities  

Have you looked at hollow-core concrete planks as an alternative? The 1st floor will be inside the thermal envelope, so insulation is moot.

 

FWIW, I'd be using posi-joists with resilient bars and 15mm acoustic control plasterboards below, and a rubber sound deadening strip atop each joist before flooring upstairs.

Just how much sound / noise do you want to get rid of?

[Nickfromwales]

Assuming ICF or masonry / cavity build? What about your target airtightness score if considering MVHR?

[nod]

30 minutes ago, Nickfromwales said:

Assuming ICF or masonry / cavity build? What about your target airtightness score if considering MVHR?

As above 

you will need plenty of ceiling height also To allow for false ceilings 

and a bigger budget Posi are so convenient 

[Nickfromwales]

Yup. And can be made to feel solid, and quiet.

[AD1]

I was initially going to do a block and beam first floor but decided to change for a number of reasons but mainly expense. 

 

The extra cost of suspended ceilings, PIR insulation, underfloor heating, screed and the B&B itself wasn't worth the extra cost for us. 

 

We liked the idea of UFH upstairs, particularly in the bathrooms but in a well insulated house the chances of actually using it is unlikely, unless you like your bedrooms at 22 degrees. We opted for electric UFH in bathrooms as a comfort. 

 

I wanted that solid feel of the B&B and so as a compromise I chose to use larger 300mm eco-joists and spaced them at 400mm centres. Using 22mm T&G flooring glued and screwed, the floor is rock solid. Use resilient bars and acoustic insulation to prevent sound transmission. Also, metal webbed joists are ideal for running services through. 

 

The beams can cause a thermal bridge so another reason we went for joists. We did a 'Tony Tray' around the joist ends within the blockwork. 

 

I house was piled foundation and required an additional 4 piles to support a B&B FF, another thing to consider. 

 

AD 

 

 

[Temp]

We have a B&B first floor and MVHR. Love it. The MVHR ducts run horizontally in the loft and down vertically into rooms so no horizontal ducts in the B&B floor. I think all the vertical sections are boxed in built in wardrobes upstairs. Never noticed a noise issue due to penetrations through the floor. 

 

The B&B company provided clips to fix battens to the underside of the beams to which the plasterboard is fixed. You just need to plan ahead so you don't have issues with the clearance for shower waste pipes. All of ours run in the insulation and screed above the B&B. 

 

Don't run vertical ducts too close to walls, the room vents are sometimes a bit larger diameter than the duct so the duct needs to be a few inches away from walls.

[Conor]

We used 150mm concrete planks. Off the back of a haib lorry and on to the walls in about an hour. Can't beat it.

 

Build up... Realistically you need a 150mm suspended ceiling for your services. This is the full depth to underside of the plasterboard, leaves you with about 100mm of service void. We put in 50mm accoustic roll but the planks themselves with suspended ceiling and standard PB met the BC sound requirements.

 

On top, you are talking about a 100mm build up to the finished floor, 50mm insualtion, 50mm liquid screed. There are other options. But all in you are talking a ceiling to floor depth of 350-400mm. Same would apply to block and beam, but the process is slower. Posi joists would be 300mm all in

 

51mm ventilation ducts sound like a nightmare, you'll need 2-3x more than standard 80mm ducts or even the skinny 63mm ones (therefore plenums with 2-4 sockets and bigger manifolds.)

 

If this is a new (block) build, why not put an extra course in at floor above?

[Iceverge]

Hollow core planks here too. 

 

75mm concrete. 

150mm planks. 

140mm  service void was as tight as they could manage it. 

12.5mm PB and skim 

 

It is dead quiet with carpet over the top. 

 

Next time I think pozijoists, thinner and easier to work with.