Plaster Board on Block and Beam Floor

[heating12numpty12]

I would appreciate your help again with my extension, so I need to check that my builder is following good building practice.

To explain the situation:

I have a block and beam floor and the ends of the beams are mounted on the new extension internal wall and a damp proof course.

The walls have been Celotexed and plaster boarded and will be skimmed before the floor goes down. The builder is proposing to lay a damp proof membrane over the block and beam floor and then up the walls. Then 150mm Celotex will then be laid on the DPM and then the 50mm of screed applied.

As you will see from the photograph (which I have staged with odds and sods to show the construction method being proposed) the dry-line has been fitted approx 25mm above the block and beam floor.

It’s OK to have the dry-line fitted right down to the block and beam floor?

I hope that I have provided sufficient information.

 

[John D v2.0]

The skirting board will cover it anyway.
Your real problem there is thermal bridging. It's not clear where your insulation layer is as there seem to be one either side of the internal leaf, but the floor will bridge the celotex. Normally the inner leaf would be "warm" to allow internal structural connections without bridging, and the base of the inner leaf would be an insulating block to avoid conducting the heat out to under the floor insulation.

 

[heating12numpty12]

The skirting board will cover it anyway.
Your real problem there is thermal bridging. It's not clear where your insulation layer is as there seem to be one either side of the internal leaf, but the floor will bridge the celotex. Normally the inner leaf would be "warm" to allow internal structural connections without bridging, and the base of the inner leaf would be an insulating block to avoid conducting the heat out to under the floor insulation.

Hi

Thanks for the reply. I'am afraid I am not a builder so your reply didn't mean a lot to me (my fault), any chance of a laymans explanation?

 

[John D v2.0]

1 where is your thermal insulation?
2a if it's inside the inner leaf, what stops the floor being a thermal bridge?
2b if it's outside the inner leaf, what's the celotex for?
Thermal bridge is just something non insulating that penetrates the insulation layer. It's bad because it will be cold and therefore attract condensation.

 

[freddiemercurystwin]

What do the drawings say? Looks like a bag of spanners. Why doesn't the dpm go up inside the cavity, why so much insulation on the floor, why is the cavity insulation and insulation internally?

 

[heating12numpty12]

Hi

So on the walls, we have outer brick, 100mm of fibre insulation, internal thermalite block, 50mm of celotex and finally plaster board and skim.

The 50mm of celotex on the internal wall was required by SAP's.

The floor will be made up of concrete block and beam, damp proof membrane, 150mm of celeotex and finally the 50mm of screed.

Does this help?

 

[John D v2.0]

Oh OK that's clear, well in that case you should have the bottom of the plasterboard 150mm from the blocks and make sure the floor celotex butts tightly to the wall celotex. Don't let the plasterboard penetrate the insulation, make sure it's continuous.

 

[heating12numpty12]

What do the drawings say? Looks like a bag of spanners. Why doesn't the dpm go up inside the cavity, why so much insulation on the floor, why is the cavity insulation and insulation internally?

The drawings called for 100mm fibre in the walls and 50mm of celotex internally. For the floor 150mm of celeotex was required by the designer.

The dmp does not go up inside the cavity, if you are referring to my mock up photograph and the bit of black plastic with the 3 chunks of celotex on it this is internal.

 

[heating12numpty12]

Oh OK that's clear, well in that case you should have the bottom of the plasterboard 150mm from the blocks and make sure the floor celotex butts tightly to the wall celotex. Don't let the plasterboard penetrate the insulation, make sure it's continuous.

This is what I thought should be the case, i.e no plasterboard within 150mm of the block and beam floor. However, the builder and plasterers are telling me that it's OK to have the plasterboard going down to within 25mm of the block and beam floor.

Not sure what to do next.

 

[John D v2.0]

Tell them in writing that they are to do it to the specified height. If there are extra charges to do that then negotiate them to what you think is reasonable. Failing that just go in with a Stanley knife...

...for the plasterboard that is.