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Building Regulations, Standards and U-Values
The lower the U-Value the more insulation there is in a building element, (e.g a floor, ceiling or wall). Therefore the less heat loss.
Consequently, the higher the U-Value, the more heat loss you have in the home.
U-Values are important because there are certain standards according to the Building Regulations and Standards depending on location.
For example, Scotland buildings will need a lower U-Value due to the colder weather than England. Wales can get away with having a higher U-Value than England and Scotland because it is typically less cold.
The tables below show the suggested U-values in England, Wales and Scotland. Note the distinction between the domestic and non-domestic columns.
England
Domestic | Non-domestic | |||||
New Build | Existing Buildings | New Build | Existing Buildings | |||
Best Starting Point (Fabric Only) | Extension | Refurbishment | Best Starting Point (Fabric Only) | Extension | Refurbishment | |
Wall | 0.16 | 0.28 | 0.30 / 0.55 * | 0.22 | 0.28 | 0.30 / 0.55 * |
Floor | 0.11 | 0.22 | 0.25 | 0.18 | 0.22 | 0.25 |
Pitched Roof – Ceiling Level | 0.11 | 0.16 | 0.16 | 0.14 | 0.16 | 0.16 |
Pitched Roof – Rafter Level | 0.11 | 0.18 | 0.18 | 0.14 | 0.18 | 0.18 |
Flat Roof | 0.11 | 0.18 | 0.18 | 0.14 | 0.18 | 0.18 |
* A U-value of 0.55 W/m²·K is used for cavity insulation and 0.30 W/m²·K for internal or external wall insulation.
Wales
Domestic | Non-domestic | ||||||
New Build | Existing Buildings | New Build | Existing Buildings | ||||
Best Starting Point (Fabric Only) | Extension | Refurbishment | Best Starting Point (Fabric Only) | Extension (Domestic in Character) | Extension (Other Buildings) | Refurbishment | |
Wall | 0.16 | 0.21 | 0.30 / 0.55 * | 0.22 | 0.21 | 0.26 | 0.30 / 0.55 * |
Floor | 0.11 | 0.18 | 0.25 | 0.18 | 0.18 | 0.22 | 0.25 |
Pitched Roof – Ceiling Level | 0.11 | 0.15 | 0.16 | 0.14 | 0.15 | 0.15 | 0.16 |
Pitched Roof – Rafter Level | 0.11 | 0.15 | 0.18 | 0.14 | 0.15 | 0.18 | 0.18 |
Flat Roof | 0.11 | 0.15 | 0.18 | 0.14 | 0.15 | 0.18 | 0.18 |
* A U-value of 0.55 W/m²·K is used for cavity insulation and 0.30 W/m²·K for internal or external wall insulation.
Scotland
Domestic | Non-domestic | |||||||
New Build | Existing Buildings | New Build | Existing Buildings | |||||
Best Starting Point (Fabric Only) | Extension & Refurbishment * | Conversion of Heated Buildings | Best Starting Point (Fabric Only) | Refurbishment, Extension & Conversion of Unheated Buildings | Conversion of Heated Buildings | |||
A | B | |||||||
Wall | 0.15 | 0.17 | 0.22 | 0.30 | 0.18 | 0.25 | 0.30 | |
Floor | 0.13 | 0.15 | 0.18 | 0.25 | 0.15 | 0.20 | 0.25 | |
Pitched Roof – Ceiling Level | 0.10 | 0.11 | 0.15 | 0.25 | 0.14 | 0.15 | 0.25 | |
Pitched Roof – Rafter Level | 0.10 | 0.13 | 0.18 | 0.25 | 0.14 | 0.15 | 0.25 | |
Flat Roof | 0.10 | 0.13 | 0.18 | 0.25 | 0.14 | 0.15 | 0.25 |
* Column A is for extensions where the existing dwelling’s walls and roof U-values are worse than 0.70 W/m²·K in the walls and worse than 0.25 W/m²·K in the ceiling. Column B is for other extensions, upgraded existing thermal elements, non-exempt conservatories and conversion of unheated buildings.
Rafter Lengths
Have you ever wanted to know how to work out the rafter length for your roof?
Here are two ways you can do this by applying a little bit of maths depending on what facts you already know.
Method 1 – You know both the rise and run
The simplest way is to use Pythagoras’ Theorem which we have already written about here. Mathematically the rafter length, c, is found using the following equation:


For example. Rise = 1.8m, Run = 2.4m
Rafter length = √ [ (2.4)2 + (1.8)2 ] = 3.0m
The eagle-eyed will have spoted this is another example of a 3-4-5 triangle.
Method 2 – You know the roof pitch, θ, and the rise or the run.
Using a bit of trigonometry you can find the rafter length using the following equations.
Rafter length = Run ÷ cos θ = Rise ÷ sin θ
For example. Run = 2.4m, roof pitch = 45°
Rafter length = 2.4 ÷ cos(45°) = 3.39m to 2 d.p.
Any modern mobile phone will be able to perform these calculations.
There is a useful table below for your convenience.
Just multiply the rise or run by the appropriate rafter length factor corresponding to your roof pitch.
For example, if your roof pitch is 30ﹾ and your run is 2.4m then reading from the table the rafter length factor is 1.15. Multiply this factor by your run which gives your rafter length. If you want to add on a rafter foot (overhang) add this to your rafter length.
( 2.4 x 1.15 ) + 0.45 = 3.21 metre
Run Factor Overhang Rafter length
Roof Pitch | |||||||||||
10ﹾ | 15ﹾ | 20ﹾ | 25ﹾ | 30ﹾ | 35ﹾ | 40ﹾ | 45ﹾ | 50ﹾ | 55ﹾ | 60ﹾ | |
Rafter factor for rise (to 2 d.p.) | 5.76 | 3.86 | 2.92 | 2.37 | 2.00 | 1.74 | 1.56 | 1.41 | 1.31 | 1.22 | 1.15 |
Rafter factor for run (to 2 d.p.) | 1.02 | 1.04 | 1.06 | 1.10 | 1.15 | 1.22 | 1.31 | 1.41 | 1.56 | 1.74 | 2.00 |
- Part A – Structure
- Part B – Fire Safety
- Part C – Site preparation and resistance to contaminants and moisture
- Part D – Toxic Substances
- Part E – Resistance to the passage of sound
- Part F – Ventilation
- Part G – Hygiene
- Part H – Waste Disposal
- Part J – Combustion appliances and fuel storage systems
- Part K – Protection from falling, collision and impact
- Part L – Conservation of fuel and power
- Part M – Access to facilities and buildings
- Part N – Glazing
- Part P – Electrical Safety
- Part Q – Security in Dwellings
- Part R – High Speed Electronic Communications Networks
- Part 7 – Material and Workmanship
U-values are a measure of thermal transmittance and express the rate of heat transfer through any element of your building, such as the wall, roof, window or indeed any structural component. The higher the figure, the worse the thermal insulation quality. So aim to keep your U-values low.
Because the construction of these elements can vary so much depending on your design and choice of materials, the U-values vary too and hence they need to be calculated specifically for each element. The units used to express U-values are watts per m² Kelvin (W/m²K). This means that if a wall, for example, had a U-value of 1.0 W/m²K, for every degree of temperature difference between the air on the surface inside the wall and the air on the surface outside, 1 watt of heat would pass through any m².
In addition to the Building Regulations, you may be asked to comply with other guidelines including CFSH (Code for Sustainable Homes), SAP (Standard Assessment Procedures), SBEM calculations (Simplified Building Energy Model) and EPC (Energy Performance Certificates).
Door casings and linings sections
FD30 Door casing example
Standard door casing example
FD60 Door casing example
FD30 Door lining example

Fire rated internal door lining example
Laminate Flooring Installed In Horsforth, Leeds, West Yorkshire.
After fitting a new kitchen for this client, she asked me to install a new laminated floor and skirtings.
Handy Guides
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PDF Jig making collar and cutter guide