Loft insulation

MickyP10 · 14 Sep 2019

I live in a 50s bungalow and the loft is quite well insulated, but there is a portion of loft down the centre which is boarded for access and storage. This has loft insulation on top of the boards where the storage space isn't used. This is probably better than boards only but I wondered if it'd be of more use re-laid on top of the existing insulation, and leaving the boarded bit uncovered from insulation.

Or does it make no odds?

Thanks!

foxhole · 14 Sep 2019

How would it be of more use to reduce insulation coverage ?

MickyP10 · 15 Sep 2019

I would be increasing it on the non-boarded portion of loft. It depends on the insulation value of the board, hence the question.

foxhole · 15 Sep 2019

Board had virtually nill insulation properties.

Leofric · 15 Sep 2019

The optimum thickness for quilt loft insulation is about 300mm . Insulate the unused boarded area to the same overall thickness of insulation as the rest of the roof space.

StephenStephen · 16 Sep 2019

Insulation works by reducing heat transferring from something hot to something cold
The rate of this heat transfer depends on (amongst other things) the temperature difference between those two things - the higher the difference the higher the transfer rate.

So there's a law of diminishing return - the first layer of insulation has a lot more effect than additional insulation.

Where you've got existing insulation, the temperature at the top of it is pretty similar to the temperature of the air above it - little temp diff so little heat loss, so less point in adding more insulation.
Where you've little or no insulation, the temperature of the floor of the loft is relatively higher than the temperature of the air above it - higher temp diff so more heat loss.

So it's best to have the insulation evenly spread, and deep enough as Leofric says.

One thing you could do though, is lift the boards and insulate under them.

Leofric · 16 Sep 2019

StephenStephen said:
One thing you could do though, is lift the boards and insulate under them.

I assumed there is already insulation under the boards.

StephenStephen said:
Where you've got existing insulation, the temperature at the top of it is pretty similar to the temperature of the air above it - little temp diff so little heat loss, so less point in adding more insulation.

Depends on the thickness of existing insulation. If it is only 100mm then adding 200mm to give 300mm total thickness is recommended.

JP_ · 16 Sep 2019

Would it be possible to stick down some kingspan and board onto the existing loft boards and put new boards over it?

foxhole · 17 Sep 2019

jonbey said:
Would it be possible to stick down some kingspan and board onto the existing loft boards and put new boards over it?

Yes

MickyP10 · 17 Sep 2019

Thanks all. Topped up insulation on boarded area, as this had the least.

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Loft insulation

Leofric

Leofric

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