Difficulty achieving required uvalues, can I negotiate lower?

[purplemonkey]

is there any allowance for achieving worse that expected (required) u values.

for example I'm developing a rather small building, and adding 100mm or more to each side of a solid brick walls will have a great impact on the final usable space in. Same for ceiling height, they are all very low ceilings and fitting PIR under the current rafter space is going to destroy the feel of these rooms.

I keep joking that the government should allow people to achieve regulations of a certain year, like I'm building this to 1980 regulations! might get a lot more development if they did.

but yeah anyway, can these uvalues be negotiated?

 

[Notch7]

I dont think so.

Are you refurbishing a house or converting to a dwelling, ie change of use.

Can you do a SAPs test and make improvements elsewhere

 

[purplemonkey]

we have permission for external material changes. The building was falling down so we wanted to shore it up.

ultimately would like to convert to a dwelling. but not having a massive budget we are doing up as we go.

Its a studio space for now, but would like to convert to a flat in the future for ease of management.

 

[tony1851]

IMO the rules are flexible, as long as the U-value of specific elements doesn't fall below a certain value. Any improvement in insulation value has to be reasonable; for example, if extra insulation takes up excessive floor space or cuts headroom to unreasonable levels, you can have reduced levels.

 

[^woody^]

You can compensate ( but not by turning the hearing up) and for conversion work, there is the argument of only being required to do what is practical.

 

[purplemonkey]

thanks guys. once I've finished the construction work, I'll have a chat to our building control guy and see what we can come up with.

 

[oldbutnotdead]

Yes you can- somewhere in the approved docs there's some numbers (if the room volume or area would be reduced by more than x% then you don't have to go the whole hog). Any reason you can't go for external insulation?

 

[purplemonkey]

the external walls fall on other property lines. I would have to seek permissions for the extra 110mm... which might be harder than talking to building control.

but thanks for the heads up on the approved docs. I don't suppose you have any more clarity?

 

[tony1851]

The Approved Docs. on thermal insulation requirements are not easy to navigate as they are based on performance standards rather than specific insulation thicknesses and if you are not familiar with them, you will end up scratching your head. (In the old days when insulation was not regarded as important, the regs would give acceptable thicknesses of insulation for walls and roofs depending on the type of insulation used).
Unless you are into pain and want to learn some number crunching, you may be best in the long run seeing what your inspector suggests, while pointing out to him the practical difficulties you face with headroom and floor area. In this respect, private inspectors are often more accommodating than local authority bods.

 

[oldbutnotdead]

Page 19 Section 5.2 (see if this Paste works. Nope.
Walls- if the internal floor area would be reduced by more than 5% by fully compliant insulation then a lesser provision may be appropriate
Floors- a lesser provision may be appropriate where meeting the standard would create sgnificant problems with adjacent floor levels
Ceilings- nowt written, can you not insulate between the rafters (are we talking flat roof or vaulted roof- your original post implies no joists). If full insulation would drop the ceilings below 2400 then most inspectors would look at a compromise (though the ceiling insulation is the important one in energy saving terms)

 

[lt8480]

Old solid brick walls breathe and absorb/release moisture.

Upgrading them has two trains of thought:

Approach 1. Membrane/DPC batten the brick wall, insulate and add a vapour control layer on the warm side of the insulation. This approach assumes the brickwork still has lime mortar (which it often does not and instead has been repointed with cement based mortar) and also no cement render externally (lime render would be fine) so that any rain on the wall can dry outwards (e.g. Kingspan's approach). The VCL traps any room moisture on the warm side of the insulation so it cannot condense within the wall.

Approach 2. Breathable insulation and breathable lime based renders, paint etc. (no cement) to allow the wall to continue to breathe/dry in both directions. (e.g. woodfibre). If you do this then too much insulation can actually cause condensation problems within the wall, but some argue better to maintains the functioning of a historic wall. You can use this approach to argue a lower u-value. However, it doesn't really yield thinner walls as is lesser performing compared to say Kingspan's insulated plasterboard.

If say a poor quality cement render has been applied externally and keep cracking and approach 1 is applied then water will track into the wall and won't be able to dry outwards (so has to force dry inwards), damp will then appear internally - in these instances you may be better to use approach 2 to help the wall dry more evenly - of course the render should also be repaired / ideally stripped and/or replaced.

If you go less than the standard u-value manufacturer's often don't publish the build-ups, therefore make sure to check things like condensation risk etc. with the manufacturer (especially in dual layer insulation systems) as simply omitting one layer or thinning one layer down only could cause all sorts of condensation problems.