Any experience of exemption from Part L building regs for a historic building?

[Tigg]

Hi all - this is my first post here, so be kind

 

I have a very tiny barn in cornwall, where I'm from - it's over 150 years old, not listed, but it is in a conservation area, a traditional barn for these parts, made of granite, and in a mess - unused for probably 50 years or so, needs a change of use applied for, and in doing that we'll be asked how we're going to comply with insulation regs - sometimes it seems in these circumstances owners are expected to match new-build standards, but my argument would be that this has always been a breathable building, and to put 200mm of PIR everywhere will stop it breathing, leading to problems - it will also nab a large amount of the available space, as this barn is really tiny - so I'd be asking for the historic nature of this barn to be taken into account, including its breathability, and then asking that we use other insulation materials, probably aerogel in some form (I know, it's VERY expensive, but this is a tiny barn) - we can show calculations that would prove we were doing the best we could without damaging the fabric of the building, but has anyone out there actually DONE THIS????? in terms of speaking to building control, persuading them that you don't have to match new build regs, doing your best to get as close as possible to the regs etc - have you done this and how did you do it? I'd REALLY appreciate any experience anyone has of this tricky area - thanks very much - nick

[Mike]

Welcome!

 

There are some exceptions in Part L of the Building Regulations for 'listed buildings, buildings in conservation areas and scheduled monuments' and for 'historic and traditional dwellings'. However they only apply when the work would 'unacceptably alter the dwelling’s character or appearance' - in which case 'the work should comply with standards in this approved document to the extent that it is reasonably practicable'.

 

In theory you might qualify under the first of these, but in practice it's unlikely to help; it's more for when insulating internally and externally are both ruled out for heritage reasons, or double glazing can't be retrofitted to historic windows.

 

In theory the second case wouldn't apply as it's a barn, not an existing dwelling, but the Local Authority may be flexible on that if they want to see it put to use as a house.

 

22 minutes ago, Tigg said:

but my argument would be that this has always been a breathable building, and to put 200mm of PIR everywhere will stop it breathing

Don't use PIR. Vapour-permiable options are readily available and advisable - you'll find some topics on this forum.

 

In a renovation there are provisions for when the the full insulation standards can't be met but, from memory, they wouldn't normally apply in a conversion.

 

28 minutes ago, Tigg said:

aerogel

Is unlikely to be financially viable outside the World's major cities, where the property value /m² of floor area gained exceeds the cost of Aerogel.

 

25 minutes ago, Tigg said:

it will also nab a large amount of the available space, as this barn is really tiny

That's not an argument that will fly; you'll need to use clever design to maximise the space that is available.

 

Sounds like you need to find yourself a local architect experienced in restoring / converting old buildings.

[sgt_woulds]

Only use unnatural insulations if you are fitting them yourself and can absolutely confirm every detail of installation is impecible, interstitial damp and misery awaits unless you get very lucky with your builders.  A poorly installed but breathable natural insulation will generally give less long term issues than a badly installed unatural and non-breathable one.

 

It is important to note that companies that make natural insulations do not generally recommend achieving high U-values with IWI due to the condensation risk to the structure.  There is, generally, a sweet spot between 40-100mm of woodfibre that balances the energy savings, cost, and condensation risk. 

 

Part L of the Building Regulations for England offers flexibility when retrofitting existing walls, roofs and floors; an improved U-value of 0.30 W/(m2·K) is the target but a ‘threshold’ level of up to 0.70 W/(m2·K) is sufficient, as long as the approach can achieve a payback not exceeding 15 years and is ‘technically and functionally feasible’. 

 

There is also a provision in the regs if IWI will reduce the floor area by more than 5% where lower insulation levels are allowed, but honestly, if your barn is that small then you will need to look at alternatives to conventional insulation anyway.

 

Unfortunately these allowances only really apply to an existing residence and are harder to swing for a conversion, but it is worth discussing with your local authority / BCO.  For an older building, most BCOs are now sympathetic to the argument that breathability is more important than the ultimate insulation value.

 

IWI requires careful consideration; the breathability and condition of the walls and pointing should be assessed before specifying the insulation solution.  The best advice is to have the external walls assessed via hygrothermal software -  such as WUFI - which will take all of the site variables into account.  Internal wall insulation is more complicated than external insulation due to the way it moves the dew point within the construction.  In addition, standard U-value calculations will not correctly account for the sorption properties of natural insulation fibres, nor their ability to pass on liquid water through capillary action.  WUFI purely considers moisture issues and how the various elements of the building fabric will deal with the volumes based on site-specific conditions.   This is the evidence you need to convince BCO of your inentions.

 

These may help:

 

Rethinking IWI with Natural Fibre Insulation

 

Insulation and retrofit - Finding the sweet spot - The Alliance for Sustainable Building Products (asbp.org.uk)

 

The-use-of-natural-insulation-materials-in-retrofit.pdf (stbauk.org)

 

 

I can also recomend Back to Earth as they not only have a lot of experience with insulating historic buildings but can provide the WUFI assessment too.  

 

Edited Wednesday at 09:17 by sgt_woulds
poor grammer

[Roger440]

As already indicated, there are exemptions for retrofit. But a conversion is treated as a new build as far as im aware.

 

Saveasteading is probably the person to answe this?

[ADLIan]

BR standard for conversion work is lower than for new build plus relaxations outlined above. Get the conservation officer on your side I believe he can trump building control if building is listed, historically important or in conservation area.

11 hours ago, sgt_woulds said:

It is important to note that companies that make natural insulations do not generally recommend achieving high U-values with IWI due to the condensation risk to the structure.  There is, generally, a sweet spot between 40-100mm of woodfibre that balances the energy savings, cost, and condensation risk.

I’d have a lot more confidence in these companies if they knew the difference between a high and a low U-value.

[sgt_woulds]

 

14 hours ago, ADLIan said:

BR standard for conversion work is lower than for new build plus relaxations outlined above. Get the conservation officer on your side I believe he can trump building control if building is listed, historically important or in conservation area.

I’d have a lot more confidence in these companies if they knew the difference between a high and a low U-value.

 

 

 

🙃 Slip of the keyboard, sorry!