Extension Plans Lytham 
Extension Plans Blackpool

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House Plans Blackpool 

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A Discussion about Heat Loss from Your Extension

Extension Plans Blackpool


In the attempt to achieve Net Zero the government makes sure that the Building Regulations insulation values are regularly upgraded  to achieve a better level of heat loss from your new extension.

This is done by a requirement to increase the amount (or type) of insulation in the Roof, Walls and Floor.

It is important to remember that these upgrades make the heat loss from the structure less. So monies spent on heating are saved because of this.

The most recent change to the Building Regulations was on the 15th June 2022 which meant that any plans that were submitted for approval after that date had to meet this new requirement.

The insulation product insulation value is measured as a thermal resistance (msqK/W) value.

When the insulation (of a certain thickness) is combined with other elements of that part of the building, for example a wall, all the elements (outer leaf, cavity, cavity insulation, inner leaf, plasterboard), have their values calculated to give a U value (/MsqK) for that makeup.

The table below shows what the changes were on 15 June 2022

The table below gives a comparison between the new and previous requirements of
the Part L document which went into effect on 15 June 2022.

There are other elements, but I think you get the point.

So for example an external cavity wall with a brick outer leaf and a block inner leaf with plasterboard and skim internally has had its insulation increased in thickness to meet this new U value of 0.18 /MsqK.

The insulation thickness is now a minimum of 90mm whereby it used to be 50mm.

There is also a need to assess where the extension is being built, as if it’s in a coastal area there would be a possibility of driving rain, this means that the clear cavity needs to be retained as being 50mm. (in non coastal areas a full fill cavity insulation can be used i.e. losing the clear cavity).

These changes of thickness of the insulation and cavity makes the overall wall thicker than it used to be.  Previously a total thickness of 315mm NOW a total thickness of 369mm is required.

It is important that your builder is aware of these changes as the consequences of building the structure using the old values is dire. The building inspectors who do an inspection would ask that the structure be made to meet the new values. This can be done by applying (fixing ) a combined insulation/plasterboard liner to the inner face and this would add another 100mm to the wall thickness. This is of course an additional cost with possible redecorating.

I hope this lets you know the importance of getting your plans and specifications done by someone who is up to date with the Building Regulations. Also using a recommended builder who isn’t ‘old school’ i.e. using out of date insulation values.

For additional information contact Chris at Homeplan Designs

T:-  01253 737724

M:- 07971 293182

Email: cnsinkinson@gmail.com

Extension Plans Blackpool