Suspended floor design

[baldnotyet]

Hi

Am installing a new ground level suspended floor and need some help on design aspects. I understand that there are some key elements to incoporate in the design but am not sure about some aspects and would appreciate input on these.

Underfloor ventilation. From what I've read cross ventilation is ideal. However, my house design will only allow air bricks on two walls that are not opposite each other. Is this fatal/is there a way to compensate?

Floor ventilation. Is this entirely necessary as it seems a sure way to introduce draught into the house?

Ground moisture barrier. I am not planning a concrete slab and the walls have already been built. Will a black PVC sheeting simply laid on the bare earth soil act as an adequate moisture barrier? Is it fatal if one leaves the bare earth uncovcered?


Insulation. My idea is to lay some insulation between the joists. Does one have to be careful about the type of insulation?

Vapor barrier. In my readings on the topic there has been frequent reference to placing a vapour barrier on top of the insulation, which I assume is on top of the joist and therefore immediately below the wood floor. Is this necessary if one has a moisture barrier on the ground and wouldn't this barrier lead to condensation forming just underneath the wooden floor?

Sub floor. Some articles refer to a sub floor beneath the wood floor. I like the idea as it seems a good way to deal with draught and also to provide an xtra layer of insulation. Has anybody any experience with this? Does this not lead result in condensation?

Draught proofing. What's the best way of draught proofing without introducing condensation?



Anything essential I have not mentioned?

Cheers

 

[freddiemercurystwin]

Underfloor ventilation. From what I've read cross ventilation is ideal. However, my house design will only allow air bricks on two walls that are not opposite each other. Is this fatal/is there a way to compensate?

If you can only achieve it on non opposite walls so be it.

Floor ventilation. Is this entirely necessary as it seems a sure way to introduce draught into the house?

Yes or the joists will rot, the insulation needs to be jammed into the gaps between the joists, any gaps sealed up with expanding foam.

Ground moisture barrier. I am not planning a concrete slab and the walls have already been built. Will a black PVC sheeting simply laid on the bare earth soil act as an adequate moisture barrier? Is it fatal if one leaves the bare earth uncovcered?

A light concrete slab either drained & to a fall or above the surrounding ground level is required beneath the suspended floor to comply with Building Regulations. You don't need a moisture barrier as the void is ventilated and any damp air will be extracted via the vents. You just need a dpm in the walls beneath the joists.

Insulation. My idea is to lay some insulation between the joists. Does one have to be careful about the type of insulation?

Choose a Rigid insulation designed for the job such as Kingspan K3.

Vapor barrier. In my readings on the topic there has been frequent reference to placing a vapour barrier on top of the insulation, which I assume is on top of the joist and therefore immediately below the wood floor. Is this necessary if one has a moisture barrier on the ground and wouldn't this barrier lead to condensation forming just underneath the wooden floor?

You don't need a vapour barrier in a suspended timber floor.

Sub floor. Some articles refer to a sub floor beneath the wood floor. I like the idea as it seems a good way to deal with draught and also to provide an xtra layer of insulation. Has anybody any experience with this? Does this not lead result in condensation?

What do you mean by a sub floor?

Draught proofing. What's the best way of draught proofing without introducing condensation?

This has been covered already, ensure the insulation is sealed to the joists.

Anything essential I have not mentioned?

Probably.

 

[baldnotyet]

Thanks for the feedback Freddy's twin - greatly appreciated.

I put in the bit about the sub floor as I picked it up from a post on WoodfloorOnline.com on suspended flooring. Not sure what the material would be but I presume some sort of plywood. The post had the sub floor on top of the joists, a layer of felt of some sort and then the wood.

"A light concrete slab either drained & to a fall or above the surrounding ground level is required beneath the suspended floor to comply with Building Regulations."

In my part of the world Building Reg's don't specify this. Am a bit worried about this as building process is quite advanced and there is no concrete slab planned. What is the danger of omitting this slab?

"You just need a dpm in the walls beneath the joists. "

How far beneath the joists and how continuous around the supporting wall?

 

[freddiemercurystwin]

Just where in the world are you?