1. Prepared by Frank Cooney B.Arch MRIA
BUILDING REGULATIONS – TECHNICAL GUIDANCE DOCUMENT: PART L, Conservation of Fuel and Energy - Dwellings
Prepared by Frank Cooney B.Arch MRIA
Existing c.1850 House With An Extension.
Existing House Is Not A Protected Structure.
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4. An Victorian terrace house which is not a Protected Structure.
Case Study 1
An Victorian terrace house which is not a Protected Structure.
No Extension.
No Material Alterations.
No Window Replacement.
No Boiler Replacement.
Existing Energy rating - F
Part L applies to existing buildings where a Material Alteration takes place.
Part L applies to the specific element that is changed when a Material Alteration occurs.
What is a Material Alteration?
Conclusion
For this example no Material Alterations, therefore Part L does not apply.
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5. Case Study 2 Extension To Rear New Opening In Rear Wall
No Works To Existing Building
No Window Replacement
No Boiler Replacement
Part L applies to the extension
Part L applies to the opening in the rear wall as it is a Material Alteration.
Part L does not apply to the remainder of the existing house.
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6. Conclusion
Fabric Insulation: U-Values for the extension are those which apply
to a new build. See Table 1 TGDL
CO2 Emissions: Not applicable.
DEAP calculation not required for extension.*
- DEAP calculation must be carried out on the entire dwelling if it is
being sold.
Thermal Bridging: Should be limited/omitted. ‘Reasonable care’.
Use ACD’s.
Air Tightness: ‘Reasonable care” should be taken to ensure unwanted
air infiltration does not occur. Use ACD’s.
Space and Hot Water Heating Systems: Existing not being altered as
boiler has sufficient capacity, therefore Part L does not apply.
If extension is separated from house by door/glazed screen, and if it
contains a heating facility it must have provision for automatic
temperature and on/off control.
Hot Water Storage Vessels, Pipes and Ducts: Existing not being altered,
therefore Part L does not apply
Ventilation: Background ventilation required to comply with Part F of the
Building Regulations.
* We recommend that a DEAP calculation is carried out regardless of Part L non requirement
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7. Refurbishment of the Existing House with no extension No Extension.
Case Study 3
Refurbishment of the Existing House with no extension
No Extension.
Windows Replaced
Boiler replaced
Internal Structural Wall Removed
Part L applies to works on the windows and boiler only.
The removal of the wall is a Material Alteration, however Part L does not
apply as it is an internal wall.
Part L does not apply to the rest of the house as works are deemed to
be repair and renewal, no material alterations occur.
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8. Conclusion
Fabric Insulation: U-Value applies to windows only. The maximum
U-Value permitted is 1.6W/m2K (Table 5)*.
CO2 Emissions: Not applicable.
DEAP calculation not required but it is recommended.
Thermal Bridging: Applies to windows and reveals.
Air Tightness: Applies to windows and reveals.
Space and Hot Water Heating: - Part L does apply.
- Boiler must be of 90% efficiency.
- Controls/Zoning
- Lagging and insulation.
Ventilation: Background ventilation required to comply with Part L**.
Upgrading sliding sash windows to 1.6W/m2K is a challenge.
** Increased condensation risk.
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9. Case Study 4 (What was actually carried out.)
Structural Works Carried Out - Material Alteration.
B1 Rated. ( 10 kilowatts short of A3).
Comprehensive Upgrade of Existing Fabric - Existing Fabric In Very Poor Condition.
- Existing roof timbers deteriorated, old non breathable felt.
- Lime plaster to walls delaminated.
- Some existing walls previously dry lined with plastic sheeting resulting in rot in joist ends.
- Floor joists ends rotten
- Moisture ingress at basement/lower ground floor level
- Windows in poor condition
- Heating system - fire and storage heaters only
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10. Part L applies to the extension.
Part L applies to the existing building.
Part L applies to the replacement boiler and windows.
Conclusion/Works Carried Out to Existing Building
Fabric Insulation: Roof U-Value required, 0.25W/m2K, Actual
U-Value achieved, 0.16W/m2K.
Gutex on existing rafters. Cellulose between rafters with
‘intelligent’ air tightness membrane.
External Walls: U-Value required, 0.55/0.35W/m2K, U-Value
achieved, 0.31W/m2K.
- Plasterboard, not foil backed, on ‘intelligent’ air tightness
membrane. Thermally broken metal stud with breathable
insulation. Detailed condensation risk analysis carried out,
quality control at installation of membrane.
- Ground Floor: U-Value required, 0.45W/m2K. U-Value
achieved, 0.18W/m2K.
Concrete on 200mm insulation on tanking membrane.
Quality control re: detailing to eliminate cold bridges and
achieve continuous air tightness.
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11. - Windows: Sliding sash restored
- Windows: Sliding sash restored. Double glazed using system approved by
Scottish Heritage. Air tightness at shutters and wall junctions.
CO2 Emission: DEAP calculation carried out.
Thermal Bridging: Detailed analysis using Therma/Wufi software. Careful
detailing to avoid cold bridging and condensation.
Air Tightness: Internal air tightness membrane. Air tightness/’intelligent’
membrane - Quality control systems/continuity.
- ‘Balloons’ fitted in existing chimneys.
Blower Door Test: 1.8 m3/hr/m2 - ‘ Balloons’ in chimneys - HRV fitted
Solar Thermal - subject to Planning Permission - 600ltr buffer tank- 5
heating zones- thermostats on all zones

12. Conclusions/Works Carried Out To Extension
Fabric Insulation: - Roof U-Value required, 0.16W/m2K. U-Value achieved, 0.14W/m2K.
- Wall at upper ground floor, timber frame. U-Value required, 0.21W/m2K.
U-Value achieved, 0.12W/m2K.
- Wall at lower ground floor, wide cavity masonary construction. U-Value
required, 0.21W/m2K. U-Value achieved 0.13W/m2K.
- Lower ground floor, raft foundation on super grund. U-Value required
0.21W/m2K. U-Value achieved, 0.18W/m2K.
- Triple glazed 0.8 U-Value windows to rear, restored sliding sash to front.
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13. CO2 Emissions: DEAP calculation carried out for extension and existing
dwelling.
Thermal Bridging: Therma/Wufi analysis carried out on all details.
Air Tightness: Internal air tightness membrane. Air tightness/ ‘intelligent’
membrane - quality control systems/continuity.
Blower Door Test: 1.5 air changes. - ‘ Balloons’ in chimneys - HRV fitted
Solar Thermal - subject to Planning Permission - 600ltr buffer tank- 5 heating
zones- thermostats ion all zones
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14. does not apply to the existing dwelling which remained untouched.
Conclusion:
Case Study 1: Repair and Renewal - Part L does not apply as no Material Alteration took place.
Case Study 2: Extension to Rear - Part L applies to the extension and rear wall of the existing
dwelling as a material alteration occured in the form of an opening. However it
does not apply to the existing dwelling which remained untouched.
Case Study 3: Refurbishment of the Existing House with no Extension - Part L applies to the
works on the windows and boiler only. Part L does not apply to the rest of the
house as works are deemed to be repair and renewal, no material alterations
occur.
Case Study 4: Refurbishment of Existing and Extension to the Rear - Part L applies to the
entire dwelling, the extension and the existing as Material Alterations were
carried out. The U-Values of the existing dwelling must comply with Table 5
of TGDL and the U-Values of the extension with Table 1 of TGDL.
Part L also applies to the boiler and all windows.
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15. Frank Cooney B.Arch MRIA
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