Proposed works
Reason for works
The need to reduce the air leakage rate and improve the thermal performance of the pitched ceilings of the roof are the main drivers in setting out the proposed minor renovation. Replacing the modest amount of external wall insulation to the kitchen and insulating the wall it shares with the unheated garage (for the first time) are also practical measures with no heritage impact.
Secondary glazing is proposed as a way of greatly increasing the airtightness at the windows, with secondary and tertiary benefits of reducing heat loss and reducing risk of surface condensation by raising the temperature of the coldest room surface (i.e., the window frame and glass). Insulating the pitched ceilings will greatly reduce heat loss (particularly radiative heat loss on cold, clear winter nights), but it also gives a chance to address the issue of the collapsed parging plaster and the lack of an air and vapour control layer (AVCL).
If the larger roof works (major renovation) are done instead of the roof insulating works (minor renovation), they would allow the room plasterboard to be retained while the roof membranes, insulation and slating are done from the outside: a better job but a bigger budget. That major renovation project would also feature internal wall insulation for the first time for most of the house using an insulating lime-cork slurry that is hygroscopic and capillary active but can also round corners so that a subtle but key aesthetic feature of the inside of the house can be preserved.
Exploratory essays
Two of these works are explored further in exploratory essays
- Choosing an appropriate internal wall insulation for a solid wall [link to follow]
- Historic windows – secondary glazing case studies [link to follow]
Design
The creation of the new ‘major renovation’ standard has implications for what measures a homeowner of an existing dwelling (which is not listed on register of protected structures) may consider. In brief, renovating more than 25% of the surface area of an existing dwelling (where that includes some form of wall insulation) triggers the requirement for a cost-optimal improvement which is identified as 125 kWh/m2.a.
See Section 2.3.1 and 2.3.2 of TGD-L:2018. Section 2.3.1 states “Where more than 25% of the surface area of the dwelling envelope undergoes renovation the energy performance of the whole building should be improved to Cost Optimal level in so far as this is technically, functionally and economically feasible.
Proposed maintenance & energy-efficiency focused works
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Works summary Works completed are shaded orange/brown. Minor renovation measures are shaded orange. Major renovation measures are shaded brown. The grey shading below is a visual device to group types of works together (e.g. different types of wall insulation works). |
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Upgrade Measure |
Minor renovation measures |
Major renovation measures |
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External works, ground levels, surface drainage |
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Moisture-related maintenance work |
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Re-pointing of mortar joints |
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Re-rendering or plastering of walls |
✓ |
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Internal wall insulation |
✓ |
✓ |
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External wall insulation |
$✓ |
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Cavity wall insulation |
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Fit flue damper or flue balloon |
✓ |
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Block flues |
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✓ |
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Window maintenance |
✓ |
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Secondary glazing |
✓ |
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Retrofit double glazing to external windows |
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Windows & external door replacement |
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Draughtproofing |
✓ |
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High level of airtightness |
✓ |
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Internal redecoration |
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Insulation of suspended timber ground floor |
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Replacement insulated solid floor |
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Maintenance work to roof and drainage |
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✓ |
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Roof insulation on flat ceiling |
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✓ |
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Roof insulation on pitched ceiling |
✓ |
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Re-plumbing |
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New room heaters |
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Heating system replacement |
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Heating controls upgrade |
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Domestic hot water storage upgrade |
✓ |
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Solar hot water |
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Re-wiring |
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Change to 100% low energy lighting |
✓ |
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Standalone extract ventilation |
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Whole house demand control mechanical extract ventilation |
✓ |
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Mechanical ventilation with heat recovery |
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Description of proposed minor renovation project and heritage impact
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Item |
Description & comment |
Heritage Impact |
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Insulation on pitch |
Take down and store all T&G boarding on ceilings. Insulate with dense woodfibre between and below rafters with continuous taped variable diffusion vapour control layer and replace boarding
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None T&G boarding is not original to the house |
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Internal insulation |
Internally insulate (previously uninsulated) attic level walls of mezzanine
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None No significant features affected |
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Draught stripping |
Consider that all existing draught stripping is due replacement (focus on external doors, attic hatches, etc.) Fit flue balloons in all flues when not in use: remove if surface condensation appears or grows
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None No impact on original fabric |
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Secondary glazing |
Install robust secondary glazing to room side of all metal windows ensuring minimal impact and a significant improvement in airtightness
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Low No impact on original fabric or windows. Will ensure future retention of original steel windows |
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Services |
New factory insulated cylinder and pipe insulation (boiler and heating controls which were recently fitted under BEH Scheme to be retained)
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None |
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Ventilation |
Install humidity triggered mechanical extract ventilation system with fan in attic store accessed from mezzanine. Kitchen may have to have separate unit with fan located in garage due to difficulty connecting ducting to fan otherwise.
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Low Minimal impact on original fabric and character of house
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Description of proposed major renovation project and heritage impact
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Item |
Description & comment |
Heritage Impact |
|---|---|---|
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Includes |
All works listed in minor renovation project above |
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External insulation |
Remove 50mm of external insulation applied to garden wall of rear extension and replace with EWI sufficient to achieve 0.21 W/m2K. Extend insulation below top of flower bed by 300mm. Also insulate garage side of wall shared with kitchen (thereby making no change to fitout) with insulation to achieve 0.21 W/m2K extending insulation for one metre beyond party wall to reduce thermal bridging
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None Works are proposed to contemporary extension to rear of house |
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Internal insulation |
Internally insulate all walls with lime-cork composite slurry or woodfibre such that rounded corners can be maintained. 0.35
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Low |
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Garage wall |
Insulate garage wall 0.21 |
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Flat roof |
Strip kitchen roof and insulate over and re-apply membrane. 0.15
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None Work relates to flat roof of contemporary extension to rear of house
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Main roof |
Remove all slates, store, apply new taped breather membrane, new battens and replace roof slates. Should insulation on pitch not have taken place already, this is an ideal chance to access roof from both sides, optimising quality. |
Medium/High Significant risk of breakage/loss of original roof finish during the works which alter the homogeneity of the street frontage.
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Block flues |
Keep flu rope for solid fuel stove. Block all others. Use vermiculite up to 200mm above the line of insulation in attic and cap chimney pots such that a trickle of air only can vent away. Use time on roof to check condition of pots and top of stack |
None No impact on original fabric |
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Heating |
Air-to-water heat pump |
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