Housing refurbishment: Airtightness

Issues

Where it all goes.....

1	Around the ends of floor joists or joist hangers
2	Beneath inner window sills and around window frames
3	Through windows and/or hollow window frames
4	Through and around doors – particularly double doors
5	Beneath doors and doorframes
6	Along the top and bottom edges of skirting boards
7	Between and around sections of suspended floors, usually timber floorboards
8	Around loft hatches
9	Through the eaves
10	Around rooflights
11	Through gaps behind plasterboard on dabs or hollow studwork walls
12	Cracks or holes through a masonry inner leaf
13	Around supplies from external meter boxes
14	Around wall mounted fan or radiant heaters; around and through fused spurs and pull switches
15	Gaps around boiler flues
16	Around water and heating pipes that penetrate into hollow floor voids and partition walls
17	Around waste pipes passing into floor voids or boxed in soil stacks
18	Around waste pipes passing through walls
19	Gaps around heating pipes
20	Around and through recessed spotlights
21	Around waste pipes, gas and water supplies, cables, which penetrate the lower floor
22	Around vent pipes passing through to loft void
23	Through MVHR or warm air heating systems; around terminals
24	Gaps around pipes to cold water and/or heating header tanks
25	Around and through wall-mounted extract fans, cooker hood vents, tumble dryer vents
	Other routes
26	Around and through ceiling roses
27	Through room thermostats and heating controllers
28	Behind polystyrene coving along wall to roof joints
29	Through key holes and where locks and bolts prevent effective draughtproofing
30	Around internal timber joists that penetrate plaster walls
31	Through subfloor air supplies to solid fuel heaters
32	Through gaps in the casings of MVHR units
33	Up chimneys, particularly where flue dampers are not fitted
34	Through airbricks and partially closable hit-and-miss vents
35	Through window spinner vents
36	Around and through closed trickle vents

 

Achieving airtightness

	Air barriers must be impermeable, continuous, durable and accessible.
	Laps in membranes should be rigorously sealed. Run a layer of double sided tape between the membranes at the overlap and run a tape over the leading edge of the outer sheet. Ensure that laps are position over a supporting area eg studs
	When installing / reinstalling a window/door frame, ensure that the gaps around the frame are sealed. Mastic is suitable for small joints, but where the openings are larger, use a compressible flexible foam. Ensure that the airtight membrane meets the seal to maintain the airtight layer overall.
	Silicon seal joints between door / window frames and the surrounding wall externally. Internally, apply sealant to gaps between the wall reveals / window boards and the window / door units.
	Draughtstrip existing windows and external doors. (Do not draughtstrip to kitchens and bathrooms unless extract ventilation is provided.) Use synthetic rubber or elastomeric tubular seals. Use brush seals with sash windows.
	Draughtstrip the loft hatch. Ironmongery should be specified to ensure seals are compressed.
	Seal holes around services passing through the external wall including water, drainage, gas pipes, boiler flues and electrical cables. (Ensure that the sealant around boiler flues is heat resistant)
	Seal holes around service pipes passing through suspended timber floors.
	Seal holes around light fittings and pull cords in the ceiling.
	Block up the fireplace and insert vent. Cap the chimney.
	When drylining directly to an external wall, apply a continuous perimeter of adhesive. Ensure the joints beween boards are sealed
	Lay room-conditioned hardboard over existing square-edged floor boards. Seal the perimeter.
	Seal the joint between the ceiling and the external wall
	If in good condition, existing lath and plaster ceilings can be retained. This cuts down on materials and reduces waste.

 

The designer's work plan

The role of the designer is critical. Design for air tightness should be simple and buildable. Targets should be achievable. Roles and responsibilities should be established at an early stage. The Contractor should be made responsible for achieving the designed airtightness levels.

RIBA Work Stage	Design Team Tasks
A Appraisal	Establish appropriate air permeability rate
B Feasibility / Briefing	Note Microclimate Test existing buildings / building to be refurbished Identify procedure for review and testing
C Outline proposals	Consider air tightness issues in relation to decisions about form of construction
D Detailed Proposals	Identify requirement of additional consultants / design by specialists
E Final Proposals	Ensure co-ordination between Design Team to ensure air tightness envelope & penetrations Detailed application of airtight materials, junctions, service penetrations
F Production Info	Select sub-contractors for specialist works (incl. testing) Careful specification of components, membranes, materials Emphasise methods for airtightness on documentation Emphasise responsibilities in specification for dealing with ‘loose ends’ between sub-contractor interfaces
G Tender Documentation	Define Contractors’ responsibilities for co-ordinating work sequences
H Tender Action	Ensure selected tenders include adequate airtightness procedures
J Mobilisation	Brief all involved in areas critical to air infiltration before work starts Preparation of samples, training, testing and QA procedures
K-L Site Works	Co-ordinate inspection with Building Control if required Ensure inspection of areas to be covered Ensure audits and testing schedule is adhered to Ensure design changes do not compromise airtightness performance
M Post Completion	Obtain feedback from concerning comfort and energy consumption Carry out remedial work as required at end of DLP.
Source: Design and Detailing for Airtightness, Chris Morgan, SEDA 2006

 

Testing

• Air testing is a crucial tool in determining the effectiveness of an air tightness strategy
• Air testing is carried out when the envelope is complete. If possible, it is wise to test twice - once before the covering-up of the membrane when remedial work can easily be carried out, and again at completion.
• Testing will identify the overall 'leakage' of the building as well as identifying individual leakage paths.

Downloads

• Design and Detailing for Airtightness, Chris Morgan, SEDA, 2006
• Improving airtightness in dwellings GPG224, Energy Saving Trust, 2005
• Energy efficient refurbishment of existing housing CE83, Energy Saving Trust, 2004
• Refurbishing dwellings - a summary of best practice CE189, Energy Saving Trust,

Standards

British Standards Institute (BSI)
• BS 7386: 1997 Specification for draughtstrips for the draught control of existing doors and windows in housing (including test methods)
• BS 5925: 1991 Code of practice for ventilation principles and designing for natural ventilation
• BS 4255: Rubber used in preformed gaskets for weather exclusion from buildings Part 1: 1986 Specification for non-cellular gaskets .

International Organisation for Standardisation (ISO)
• ISO 6589: 1981 Nr permeability of joints, watertightness
• ISO 6613: 1980 Nr permeability of tests on windows and doors
• ISO 9972: 1996 Thermal Insulation – Determination of building airtightness – fan pressurization method

Chartered Institute of Building Services Engineers (CIBSE)
• Measuring Air Permeability of Building Envelopes. CIBSE Technical Memorandum ATTMA TS1

Building Research Establishment (BRE)
• BR 359 Airtightness in UK Dwellings: BRE’s test results and their significance. 1998
• BRE Digest 306 Domestic Draughtproofing: Ventilation Considerations

Further information

• BRE, Airtightness and leakage
• BSRIA, Airtightness for Builiding Regulations

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