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Recommended U-Values for building elements


There are regulations governing the thermal properties of new, extended and renovated dwellings in Ireland and the United Kingdom.  The thinking is that:
…. buildings shall be designed and constructed so as to ensure that the energy performance of the building is such as to limit the amount of energy required for the operation of the building and the amount of CO2 emissions associated with this energy use insofar as is reasonably practicable.
Building Regulations (Part L Amendment) Regulations 2008 (S.I. No. 259 of 2008) Technical Guidance Document L – Conservation of Fuel and Energy – Dwellings

Irish Building Regulations - "Part L"

It is intended that the Irish standards specified in the 2008 regulations will be tightened further in 2010. The aim is to achieve zero carbon emissions associated with the operation and use of dwellings, at the earliest date practicable.  So today’s guidance should be regarded as acceptable for today but not future proof. 

Below are the current U-Values from the 2008 “Part L” building regulations

Maximum average area-weighted elemental U-value (W/m2K) – existing dwelling

Fabric Elements

Extensions

Material Alterations
or Material Change
of Use

Roofs
Pitched roof
- Insulation at ceiling
- Insulation on slope
Flat roof

 

0.16
0.20
0.22

 

0.35

Walls

0.27

0.60

Ground Floors

0.25

0.60

External doors, windows
and rooflights

2.00

2.00

 

The draft 2010 Part L Irish Regulations

The Irish 2010 Draft Part L has tougher U values than the 2008 figures. The proposed changes are have a * beside them.

Fabric Elements

Extensions

Roofs
Pitched roof
- Insulation at ceiling
- Insulation on slope
Flat roof

 

0.16
0.16 *
0.20 *

Walls

0.21 *

Ground Floors

0.21 *

External doors, windows
and rooflights

1.6 *

 

UK Building Regulations - "Part L"

In the United Kingdom the picture is the same.  There is also a “Part L - Conservation of fuel and power” of the UK building regulations.  These documents are available online from the UK Planning portal
Based on the 2006 values the current required U-Values are as follows:


Element

Area-Weighted U-Value

Limiting U-Value

Wall

0.35

0.70

Floor

0.35

0.70

Roof

0.25

0.35

Windows & doors

2.2

3.3

 

In the UK as well as in Ireland these "Part L" building regulations are tightening up.  The UK Department of the Environment have published  Proposed 2010 values in an updated 2010 “Part L document”


Element

Standard W/m2K

Wall

0.26

Pitched Roof Insulation at ceiling level

0.16

Pitched Roof Insulation at rafter level

0.16

Flat roof or roof with integrated insulation

0.16

Floors

0.22

 

UK & Ireland Building Regulations - The Trend

When we look at the UK and Ireland regulations together we can see that there is a gradual tightening of the requirement.  The chart below is based on the information in the tables above, but just considers the U-Values for walls. The final two data points correspond to the stated objectives of both countries to move to Zero Carbon / Carbon Neutral homes in the near future.

 

U-Values for Walls trend in the UK and Ireland - Especially External Insulation

Note * means estimated, these regulations have not been finalised yet.

Looking at the trend it can be concluded that the amount of external insulation required on Irish homes will continue to increase in the years to come. Zero carbon houses are just a few years away from being manditory for all new builds and then the push will be on to retrofit all homes to the passive house standard. . 

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