Proposed works
Reason for works
The front wall is currently experiencing moisture stress due to poor-quality failing cement jointing, tanking on room side of wall and the modern impermeable floor slab. Works will facilitate drying to the room and thus will lower the water content in the wall.
As it is 25 years since the last significant body of maintenance and retrofit work was completed, a range of repair and/or replacement works are required regardless of a specific focus on energy efficiency. The owners are also aware that during the winter months, there can be a lack of thermal comfort as the house has a poor ability to retain heat due to lack of airtightness and insulation.
Design
The creation of the new ‘major renovation’ standard has implications for what measures a homeowner of an existing dwelling (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. See 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
|
Upgrade Measures |
Minor renovation |
Major renovation |
|---|---|---|
|
External works, ground levels, surface drainage |
N/A |
|
|
Moisture-related maintenance work |
✓ |
✓ |
|
Re-pointing of mortar joints |
✓ |
✓ |
|
Re-rendering or plastering of walls |
✓ |
✓ |
|
Internal wall insulation |
|
**✓ |
|
External wall insulation |
|
✓ |
|
Cavity wall insulation |
N/A |
|
|
Fit flue damper or flue balloon |
✓ |
✓ |
|
Block flues |
|
✓ |
|
Window maintenance |
✓ |
✓ |
|
Secondary glazing |
##✓ |
##✓ |
|
Retrofit double glazing to external windows |
N/A |
|
|
Windows & external door replacement |
|
✓ |
|
Draughtproofing |
✓ |
✓ |
|
High level of airtightness |
|
✓ |
|
Internal redecoration |
|
✓ |
|
Insulation of suspended timber ground floor |
N/A |
|
|
Replacement insulated solid floor |
|
✓ |
|
Maintenance work to roof and drainage |
|
✓ |
|
Roof insulation on flat ceiling |
✓ |
✓ |
|
Roof insulation on pitched ceiling |
|
~~✓ |
|
Re-plumbing |
N/A |
|
|
New room heaters |
✓ |
✓ |
|
Heating system replacement |
(1) ✓ |
(2) ✓ |
|
Heating controls upgrade |
✓ |
✓ |
|
Domestic hot water storage upgrade |
N/A N/A |
N/A |
|
Solar hot water |
|
|
|
Re-wiring |
|
|
|
Change to 100% low energy lighting |
✓ |
✓ |
|
Standalone extract ventilation |
N/A |
|
|
Whole house demand control mechanical extract ventilation |
✓ |
✓ |
|
Mechanical ventilation with heat recovery |
|
|
**to rear walls only
##to front windows
~~bathroom and garden room
(1) gas boiler for minor
(2) heat pump for major
Description of proposed minor renovation project and heritage impact
|
Item |
Description & comment |
Heritage Impact |
|---|---|---|
|
External walls |
Strip internal tanking plaster, re-point externally with lime mortar and install a physical (not injected) damp-proof course. Lime plaster inside face of wall. |
Positive The restoration of the original pointing would be a positive development. |
|
Attic |
After preparing the attic, retain whatever insulation is still in good condition and add additional layers (all to achieve a U-value of 0.13 W/m2K). Insulate pipes and water tank properly, install draughtproofing at attic hatch and any services penetrations. |
None No impact on original fabric
|
|
Front door |
Insert insulation in recessed panes of front door. (U-value improves from 2.59 to 1.23 ). |
Low This measure is additive and reversible |
|
Airtightness |
Block two chimney stacks and install damper in flue of fireplace of livingroom Consider renewal of draught seals at all windows and external doors. Install new profiled threshold at front door to create better airtight seal and protect it with traditional timber flap fitted to outer face of bottom rail. Resulting change in airtightness proposed: Q50 target = 4.5 m3/hr/m3 |
Low New profiled threshold can usually be installed on existing saddle or floor edge |
|
Ventilation |
Fit a whole-house demand-control mechanical extract ventilation system. Humidity-triggered wall-mounted vents to be located in ‘dry’ rooms (i.e., living rooms and bedrooms). Internal finish of vents is discrete and can be colour matched. Humidity-triggered ceiling-mounted vents to be located over moisture sources in ‘wet’ rooms (i.e., bathrooms, kitchens and utility rooms). Ducts to connect extract vents to low-energy, pressure-triggered variable speed fan in attic. |
Moderate Fitting wall supply air vents will involve coring through walls and fitting vent in the front brick façade of a terraced house. Vent covers should be considered carefully to minimise impact on the façade |
|
Heating system |
Commission a proper heat load calculation from a qualified mechanical engineer or contractor to determine the size and type of boiler and heat emitters (room heaters) that will be needed for this house given (a) the volume to be heated, b) the response time required and (c) the insulation levels present after works are completed. Specify new modulating oil boiler with fully-insulated proprietary housing and highly insulated pipework. Review condition of pipe supplying boiler from oil tank. |
Low The system will be a replacement for an existing heating installation. Re-use exsting duct runs, chases, etc. where possible to minimise impact on the existing house
|
|
Heating controls |
Ensure that a ‘boiler interlock’ is achieved through use of room and cylinder thermostats, and separate time control of hot water and space heating. Locate room thermostats in living room and main bedroom away from sources of heat or light. |
None No impact on original fabric
|
|
Heat emitters / Room heaters |
Assess heat output, efficiency and location of wall-mounted radiators. Should some or all change in location, type or size? |
|
|
Hot water |
Keep factory-insulated cylinder and upgrade pipe insulation (incl. at pipe ‘knuckles’). In particular, primary pipework between cylinder and boiler should be continuously insulated |
None No impact on original fabric |
|
Lighting |
100% low-energy lighting
|
Low An increasing range of low energy lights with a warm colour temperature and shapes to allow use in historic properties are available |
Description of proposed major renovation project and heritage impact
These works are generally in addition to works described in the minor renovation above, an exception being the heat pump, which is in lieu of the gas boiler described in the minor works.
|
Item |
Description & comment |
Heritage Impact |
|---|---|---|
|
Block chimney stacks |
Block chimney stacks in dining room and two bedrooms and fit manually-operated airtight chimney damper to living room stack to rear (given that managed ventilation system is in place). See the section on chimney flues. |
Low Chimneys blocked in the manner proposed can easily be unblocked and function as fireplaces again. |
|
Ground floor slab |
Given existing moisture stress of the solid brick walls, it is proposed the existing concrete slab and DPM be removed and replaced with a breathable solid floor buildup featuring linoleum sheet on 100mm limecrete slab (λ = 0.45 W/mK) (with perimeter edge insulation) on 250mm of compacted recycled foamed glass aggregate (λ = 0,078) achieving a U-value of 0.19 W/m2K |
Positive While these works result in demolition, they should reduce moisture on the external solid walls as the floor can then share in the role of managing moisture. |
|
Front external walls |
After all works to wall described in the minor renovation works above, install a proprietary, fully bonded, woodfibre or calcium silicate internal wall insulation to ensure best drying potential of wall. A U-value no lower (i.e., ‘better’) than 0.6 W/m2K is recommended. Such insulation measures should reduce heat loss through the wall by ~60% (less than the measured U-value, 1.62 W/m2K): this is of significant energy efficiency value. |
Medium The original plain-run cornicing in the ground floor reception rooms would be lost but can be reproduced. There are no other decorative features on ground or first floor that would be affected. |
|
Rear external walls |
It is proposed that a proprietary external wall insulation system featuring mineral wool or cork-based insulation and mineral render be used. As this house has no eaves box, it is proposed that the roof be extended to meet the line of the external wall insulation. See the section on External wall insulation of traditionally built buildings for more detailed information. The works can achieve a U-value of 0.27 W/m2K. This should reduce heat loss through the rear walls by ~83% (less than the measured U-value). Note that external wall insulation carries a significantly lower hygrothermal risk than internal wall insulation retrofit. While the extension of the roof has the biggest impact, this can be done using traditional materials and methods. |
High The walls of rear of main house and the return shown in Figure 2 have few existing architectural features. Nevertheless, the external insulation will deepen window reveals and be visible at the party wall line. The alteration of the eaves will be visible in relation to the adjoining houses. |
|
Modern oriel window |
Rear timber frame oriel window: This is charming but has air gaps and is under-insulated by modern standards. Consider stripping it from outside then (a) install Intello AVCL behind room finish lapping AVCL over studs; (b) install firm quilt such as 100mm hempwool (k=0.038) between and then counter batten with 40mm woodfibre insulation batts (k=0.038) between battens (giving some thermal mass); (c) install breather membrane; (d) install vertical rainscreen battens and new TGV cladding painted. All to achieve a U-value of 0.30 W/m2K. This will result in small push out in cladding which is fine as EWI will also give new line. |
None The window is a modern addition to the original house |
|
Doors |
Upgrade existing solid four-panel door with aerogel and ply infill panels (1.23 W/m2K). Replace glazed rear door (1.40 W/m2K). |
Low The original door is being retained and a demountable insulation measure is being applied |
|
All rear windows |
By moving existing windows to the rear in a position 100mm from the face of external wall insulation, a low thermal bridging condition is created. Assume a Y-value of 0.08 W/m2K.
|
Positive Assuming an external insulation approach is being taken, moving windows and doors to rear ensures change of appearance is minimised and depth of external reveal is maintained
|
|
Bathroom pitched ceiling |
Re-roof and insulate this modern lean-to warm pitched roof to meet a U-value of 0.25 W/m2K |
None
|
|
Replacing windows (of mid-90s retrofit works) |
Replace existing timber windows to rear (featuring 6mm, air-filled double glazed units, default U= 3.1 W/m2K) and rear kitchen single glazed unit (default U = 4.8 W/m2K) with double-glazed timber sliding sash windows (featuring 16mm argon filled, low-e soft coat, warm edge spacers. U=1.40 W/m2K) |
None These windows and doors are not original |
|
Heating |
Install DAIKIN ALTHERMA3 6kW air to water heat pump in lieu of existing heating
|
None
|
|
Airtightness |
Resulting change in airtightness proposed: Q50 target = 1.5 m3/hr/m2 (0.075 ac/h)
|
Low Airtightness measures have minimal impact on existing fabric
|
External wall insulation of traditionally built buildings
For traditional solid-wall buildings built with lime, consider using an external wall insulation system with mineral wool, woodfibre or cork insulation and mineral render for enhanced breathability (especially if original lime-based render is still in place). In terms of control and quality, the system should have an NSAI or BBA agrément certificate, or a European Technical Approval (ETA), but note that systems that don’t have an NSAI agrément certificate will not qualify for grants, for example, the SEAI Better Energy Homes grant aid in place at the time of these works. While the render of the rear walls will contribute to a lower (i.e., better) U-value than the measured brick-faced front wall (1.62 W/m2K), if the performance were the same, the reduction in heat loss achieved by upgrading to a U-value of 0.27 W/m2K would be 82%. Nevertheless, it’s important that thermal bridging at eaves, ground and window junctions are also low, and that the weathertightness of the completed works is excellent.
Move any downpipes and gullies as needed to facilitate the new finished line of wall. Install proprietary external insulation system to achieve a U-value of 0.27 W/m2K and a low thermal bridging condition where attic and wall insulation meet. Surfaces around the base of the wall, such as flower beds, lawn or paviors facilitate the installation of external wall insulation 200-300mm below ground to minimise thermal bridging, while removing slates during extension of eaves facilitates the insulating to top of wall plate. Ensure continuous stop beads at sill-window and sill-wall junctions to facilitate differential movement and weather tightness. Use proper thermally broken fixings for connecting downpipes, satellite dishes, gate posts, etc.
In common with many traditional houses, this house has no eaves box: there may be no eaves fascia or the fascia may be fixed to render directly. It is suggested therefore that 1m of the roof slates are stripped along eaves and verges that are to be externally insulated. Extend roof structure locally by creating a traditional bell-cast of the slates at the eaves or a gable ladder at a gable to ensure. A bell-cast is an angling outwards of a surface similar to the change in angle at the bottom of a traditional bell. The bottom of a rendered surface often has a bell cast, and equally the last few tiles of a pitched roof. In this way, the existing eaves or verge-to-wall condition can be recreated in a long-lasting weather tight manner. This approach also allows areas of pitched ceiling to be insulated properly (an area all too often ignored or poorly insulated), and even for dwellings with flat ceilings allows a continuous meeting of wall and roof insulation. In many cases, one installer can stand on the external scaffolding while the other is inside the attic working together.
The quicker, low-cost method of installing a metal pressing (stitched back to the masonry or fascia at top and stepping out to cover the external insulation below) can look poor, is out of keeping with a historic dwelling and is vulnerable to movement and water ingress over time. The obvious and correct solution would be to extend the roof verge so a long-term weathered solution is achieved. If (a) the architect or builder are unwilling to do this; (b) it can’t be done in a sensitive manner; or (c) the homeowner is unwilling to pay the related supplement for the works, it would suggest that EWI works are not appropriate. The Bristolian Guide to Solid Wall Insulatio is an excellent resource here - Available at https://warmupbristol.co.uk/.