|Part L is different in Wales to England, so be aware of this|
Part L of the Building Regulations in Wales (and England) are basically designed around SAP and conventional U value calculations. This is fine for modern conventional cavity walled buildings, but there are issues with older solid walled buildings.
Thankfully the Approved Documents take notice of this fact and they guide you towards some additional advice. Section 12 is entitled: Dwellings of architectural or historical interest. This is broken down into 12.1 Exempt historic and traditional buildings and 12.2 Historic and traditional buildings where special considerations apply.
I think that this is where we get a bit lost, as people don't see their solid walled buildings as being 'historic / traditional'. So many think that this section will not apply to their home. This issue even applies to Building Surveyors and Architects! So wake up Wales (and other countries in the UK), many of us live in older traditionally built homes. Think of all the terraces in SE Wales, stone cottages in mid Wales and north Wales etc.
So back to the guidance. 12.2 is the big one.
“12.2.1 In addition, special considerations apply to works to the following three classes of non-exempt existing buildings:
a. of architectural and historic interest and are referred to as a material consideration in a local authority’s development plan or local development framework; or
b. of architectural and historic interest and are within national parks, areas of outstanding natural beauty, registered historic parks and gardens, registered battlefields, the curtilages of scheduled ancient monuments, and world heritage sites; or
c. of traditional construction with permeable fabric that both absorbs and readily allows the evaporation of moisture.”
So here we are at the bottom of the list 12.2.1 c. Solid walls (random rubble, solid brick etc) are 'traditional construction with permeable fabric'. So they have 'Special Considerations'.
So what are these 'Special Considerations'?
There are several that are linked to the more 'historic' side of the guidance, however there are some key paragraphs that affect your average Welsh Victorian terrace:
“Work to such buildings is required to comply with the energy efficiency requirements as far as is reasonably practicable. In considering what is reasonably practicable, the work should not unacceptably alter or mar the character of the building or increase the risk of long-term deterioration.” (p.34)
“Particular issues relating to work to dwellings of historic and architectural interest warrant sympathetic treatment and would benefit from further professional advice. These issues include: enabling the fabric of historic buildings to ‘breathe’ to control moisture and potential long-term deterioration.” (p.35)
A link to the Wales' Part 1B Building Regs can be found here
Better than this, the guidance points us towards Historic England guidance on improving energy efficiency in historic / traditional buildings.
This advice goes into a lot of detail about what to do and how. An excellent document. Worth following the link and printing it out for reference.
The missing link for many people is understanding their building. When was it built? Out of what? How has it changed over time? How significant is this? What would be the impacts of change?
There is a standardised and recognised way of achieving this: BS 7913: Guide to the Conservation of Historic Buildings (2013). This British Standard does cost money to buy, but there are a number of key issues that might be important to you and any argument that you might have with building control etc.
Energy improvements to buildings should not harm the physical performance of the fabric.
Some energy efficiency measures can have adverse effects.
Damp walls are up to one third less efficient if damp.
Correct choice of materials is really important.
Correct application of materials is also so.
Much of BS7913 is designed to help those with the more historic end of the spectrum, but it equally applies to an average terrace house (just less so in terms of architectural significance).
Basically you need to be able to understand what your building now is, how it operates, what can be done to improve it safely and considerately. This will no doubt mean that you will not be able to quickly slap a load of modern insulation all expect it to work (ECO? Green Deal?!!!)
So we have to tools and advice to help us get it right for our older buildings (especially important in Wales where we have roughly a third of all stock being 'historic / traditional'), so why aren't we using it?
Hopefully this post will give you some of the information you need to be able to make the right decisions for your home.
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