GB2478342A - Protecting a room of a building from the ingress of unwanted gases - Google Patents

Abstract

A method of collecting gas, which may be hazardous such as radon or land-fill gases, which enters buildings and collects within rooms, the method includes the venting of cavities and the room itself into a depressurized or low pressure area such as a sump H. The depressurized area may be behind a floor or wall cavity membrane, barrier F or behind a skirting board E, and the gas collected in this area may be exhausted or expelled clear or outside of the building. There may be a pump K which exhausts the gas and provides the low pressure area. There may also be a balanced ventilation system with both supply and exhaust parts which is used to achieve a design flow rate through the building and may include an automatic boost to ensure a negative pressure is maintained at the room vents.

Description

Complete Radon Protection Measures for Buildings

Background

This invention relates to the protection of the occupants of buildings against the ingress of radon gas.

During recent decades a hazardous phenomenon that is linked with the built environment has come to light. Radon gas has no taste, smell or colour and its presence is therefore not apparent, however the gas is radioactive.

Naturally occurring uranium and thorium decay to form, amongst other elements, radon gas.

The radon gas levels vary between different parts of the country but are particularly prevalent in Cornwall and Devon (Lugg and Probert, 1997). Radon in subsoil mixes with air and rises to the surface where it is quickly diluted into the atmosphere (BRE, 1993).

Concentration of radon in the open air is low, in the order of < 10 Becquerels per cubic metre of air (Bqm3). The Becquerel is a unit of radioactivity corresponding to one radioactive disintegration per second.

However, radon can enter buildings through many routes e.g. cracks in solid floors, construction joints, cracks in walls, around service pipes, through wall cavities and via the vulnerable floor/wall join (BRE, 1993). Under some circumstances the levels of radon inside buildings can become quite high.

A concentration in excess of 200 Bqnf3 is acknowledged by the government to be a health hazard to building occupants and action is recommended to reduce levels that are above this figure.

Radon has been cited as second only to tobacco smoke as the most frequent cause of lung cancer (Lugg and Douglas, 1997). Radon concentration in adjacent buildings, even adjoining ones can differ by as much as a factor of ten times so measurements from adjoining properties are not a reliable indication.

Unfortunately the current trends and government legislation for airtight dwellings in the interests of energy conservation are exacerbating the radon problem as replacement of air by ventilation has previously helped to reduce concentrations of the gas (Hollowell et al, 1980).

In particular, basements will have a higher concentration of radon than rooms above ground.

Both walls and floors of basements are in contact with the ground, therefore there is a greater potential for radon entry. Basement walls are also very often of poor quality with cracks to allow ingress, and ventilation may be very poor which allows the build up of gas.

Groundwater around basements can also contain radon (BRE, 1993).

There are six ways of reducing the amount of radon that can enter a house that has a basement: (1) Installing a radon sump system-With solid ground floors the air and radon can be extracted from beneath the floor (depressurising the soil) by using a radon sump. The most effective method. For radon levels above 1200 Bqm3 it is often the only solution (Bonnefous, 1994; Welsh, 1996).

(2) Sealing floors and walls-Passive measures whereby the floor and walls are sealed where they are in contact with the ground, preventing the radon getting through gaps and cracks.

Effective at moderate radon levels, up to 400 Bqm3.

(3) Increasing under floor ventilation -With suspended floors the flow of air can be increased beneath the floor. Effective, particularly if fan assisted up to 850 Bqm3. Not appropriate for use in houses with full basements.

(4) Installing a positive supply ventilation system -pressurise using a fan which draws air from outside or roof void and blows it indoors. Effective only at moderate radon levels, up to about 700 Bqm3, and needs an airtight dwelling.

(5) Improving the ventilation of the house -In some cases it may be possible to change the way in which the complete house is ventilated, to avoid drawing radon up through the floor or walls. This will affect the occupiers use of the dwelling and is unreliable. Effective, if at all, only at low levels of radon.

(6) Improving the ventilation of the basement -Improved natural or mechanical ventilation targeted on a basement, where the highest radon levels are likely to be, is extremely effective, and can offer large radon reductions. Mechanical fans can be used to draw air into, and/or extract air out of, a basement.

In areas where the water table is high and basements are used for extra accommodation they are often fully tanked or fitted with membranes to prevent water ingress.

It has long been thought that if a basement or cellar is to be fully tanked using mastic asphalt or some similarly impervious membrane/barrier to prevent damp/water penetration, the tanking will also provide radon protection and there is no need to provide supplementary protection (e.g. a sump) in such cases.

Unfortunately, tanking systems and membrane installations are susceptible to both poor workmanship and damage by following trades and cannot be relied upon to provide complete defect free protection.

A ruling in the High Court of Justice (Outwing-v -Thomas Weatherald) made the point that a membrane cannot be expected to achieve a total or absolute watertight bond and it acts only as one part of a waterproofing system that also incorporates sub-soil drains to relieve pressure on the membrane. A membrane that is installed with reasonable skill and care can therefore not be guaranteed to be defect free and designers must allow for this.

It is therefore necessary to design radon protection measures for basements to allow first for the possibility of radon ingress through membrane defects and secondly to enable the removal of radon which having gained entry collects at a low level within the room. As radon is one of the densest substances that remains a gas under normal conditions it can also readily move from higher levels throughout a building into the lowest areas of a dwelling, i.e. the basement.

This situation needs serious consideration when hazardous gas that may be collecting in a basement is not apparent to the senses as it has no colour, taste or smell.

Research by Zhengguo et al, 1993 showed that radon concentration is different at different positions in the same room, the highest concentrations being lower in the room. Based on the results, the radiation dose to residents when lying in a bed is 1.6 to 1.8 times that at a position 0.5 m from the ceiling and in the centre of a room the concentration at 0.88m from the floor is about 1.3 to 1.5 times that of 0.5 m below the ceiling.

Even the design of a radon protection system that uses a combination of the most effective ways, as detailed above, will still not be able to remove high concentrations of radon lying on a basement floor that have leaked past membranes or moved into the basement from higher parts of the dwelling.

The 2008 BRE Good Building Guide CBG 73 warns that in areas where there are higher levels of radon, minor imperfections in the damp-proof membrane in the floor, which also acts as a radon-proof barrier, may let through sufficient radon to cause the action level of 200 Bqm3 to be exceeded (BRE, 2008). This warning is in line with the findings of the aforementioned ruling in the High Court of Justice: Outwing-v -Thomas Weatherald Ventilation to basements is provided at a high level to prevent cold draughts which occupants find uncomfortable, any attempt to ventilate with fans at low levels will generally result in the fans being turned off (BRE, 1995).

References Bonnefous, Y.C., Gadgil, A.J., and Fisk, W. J. (1993) Impact of sub-slab ventilation technique on residential ventilation rate and energy costs. Energy and Buildings, 21, 15-22 Building Research Establishment Report BR 212. Construction of new buildings on gas-contaminated land. Published jointly by BRE, Garston, and HMSO, London, 1991.

Building Research Establishment Report. Surveying buildings with high indoor radon levels: a BRE guide to radon remedial measures in existing dwellings. Published jointly by BRE, Garston, and HMSO, London, 1993.

Building Research Establishment Report. Positive pressurisation: a BRE guide to radon remedial measures in existing dwellings. Published jointly by BRE, Garston, and HMSO, London, 1995.

Building Research Establishment Good Building Guide. CBG 73. Radon protection for new domestic extensions and conservatories with solid groundfloors. Published jointly by BRE, Garston, and HMSO, London, 2008.

Hollowell, C. D., Berk, J.V., Boegel, M. L, Miksch, R. R., Nazaroff, W. W., and Traynor G. W. (1980) Building Ventilation and Indoor Air Quality. Studies in Environmental Science, 8, 387-396.

Lugg, A. and Probert, D. (1997) Indoor radon gas: A potential health hazard resulting from implementing energy-efficiency measures. Applied Energy, 56, 93-196.

Outwing-v Thomas Weatherald. Outwing Construction Limited v Thomas Weatherald Limited. No. 1998 0 011. High Court of Justice Queen's Bench Division Technology and Construction Court, 13 September 1999, 1999 WL 1048254.

Welsh, P. (1996) Trials of radon remedies in a UK test house: An introduction. Environment International, 22, 1059-1067.

Zhengguo, Z., Liang, Z., Chunxlu, L. And Detao, X. (1993) Investigation of distribution of indoor radon concentration. Nuclear Tracks and Radiation Measurements, 22, 515-518.

Statement of Invention

To overcome the problem of low lying radon in basements and other rooms this invention proposes a method of gas collection from both structure and rooms themselves and exhausting radon to the outside air, using low level room vents that are linked either to depressurised membranes and/or their own independent extraction system. The method uses controlled basement and room ventilation to ensure that negative pressures are always maintained at the interface between vents and the room thereby ensuring continuous low level extraction of radon from the basement and/or room.

Advantages This method uses a combination of the two most effective ways of reducing radon within a dwelling i.e. depressurisation (with or without a sump) and controlled ventilation together with a new method of venting the room at low level into the depressurised space behind the membranes or skirtings in order to remove radon that collects within basements rooms.

As a result of the (Outwing-v--Thomas Weatherald) court case it is now accepted that radon can leak past defects in a membrane to enter a basement. This leakage can be via walls and or floors. There is no current effective method for removal of low lying radon in basement and rooms, existing methods concentrate on preventing ingress and are not able to purge radon from low level in a room.

Existing high level ventilation and room pressurisation are unable to purge low lying radon.

This method has a dual function in that it will first act to prevent radon ingress and secondly it is able to remove concentrations of radon that have entered the room and lie at low level near the floor.

This method handles and collects the radon and does not rely on pressurisation to hold back radon which in turn requires sealed entrances and exits and relies upon the compliance of building occupants.

The application of positive air pressure within a basement may force radon into other areas of a dwelling, whereas this method extracts the radon and exhausts it clear of the property.

This method can collect the low lying heavy radon gas to ensure a radon free basement or room in retro-fit applications where there are radon ingress problems due to defects in initial membrane installation. This is a very common occurrence as workmanship tends to suffer when the finished work is covered up by floor and wall finishes.

This method can operate as part of a fan assisted balanced ventilation system that employs powered air movement components in supply and/or exhaust sides in order to achieve a design flow rate and ensure continuous low level extraction at the room vents.

This method can be used with or without heat recovery as part of the controlled ventilation.

This method can provide adequate ventilation that is both draught and pollution free.

This method has a basic level of air flow rate for normal use and one or more boost levels under automatic control during periods of use of extract fans in kitchens or bathrooms.

Drawings The invention will now be described by reference to the accompanying five cross-sectional drawings: Figure 1 shows routes of radon entry to a basement; Figure 2 shows a membrane fitted to a basement with a sump for water and radon removal; and Figure 3 shows the new method of radon removal from inside the basement.

Figure 4 shows the new method applied to a basement or ground floor room that uses a sheet membrane for radon and waterproofing.

Figure 5 shows the new method applied to a building with only a sheet floor membrane for waterproofing, and suffering extensive radon ingress.

Detailed description

The following descriptions apply to both basements and ground floor rooms susceptible to radon ingress.

In Figure 1 a cross-sectional drawing shows the routes of entry for radon into a typical basement. In general the radon ingress for a ground floor room would be via the floor and floor/wall join. The basement wall A has cracks that allow radon ingress shown by the arrows. The basement floor B allows radon to enter the basement area at the floor/wall join and through cracks.

Radon also enters from upper floors via cracks in ceilings and when doors to the basement are opened for access. The radon will lie in the basement, greatest concentration occurs nearest the basement floor.

In Figure 2 the basement has been fitted with a waterproofing system.

The wall A has been fitted with a waterproof and radon proof cavity membrane C. The internal finish for the wall A is plasterboard D and skirting E that is sealed to the floor G. The floor B is covered with a waterprool7radon proof cavity membrane F with floor screed finish G laid over.

The sump H contains a submersible water pump J that collects water ingress from behind the membranes and it is then pumped to outside of the property.

A pump K with extract fitted at high level into sump H will extract air and radon from behind the membranes C and F and expel it from the property. The area behind the membranes is de-pressurised by the pump K. This depressurising is the most effective method for removing radon.

However, there must be consideration by the designer for defects in the membrane/barrier that will allow the radon into the basement. Radon will enter the basement via membrane defects and from higher areas of the dwelling and will collect at low level in the basement.

Neither conventional ventilation nor positive pressurisation of basement areas will remove the hazard of radon that collects at low level in a basement.

In Figure 3 to solve the problem of radon collection within the basement a series of small vents are provided at the low level floor/wall region.

The vents can be fitted into the skirting, wall or floor.

The vents will allow controlled removal of the radon that has collected in a basement due to defects in membranes and/or radon movement into the basement from higher areas of the property.

A gap where the wall membrane and floor membrane join allows the de-pressunsation produced by pump K behind the membranes C and F to also; (1) remove radon from the cavity formed between membrane C and plasterboard D; and (2) remove the low lying radon in the basement room itself via the vents that are provided, the radon is then expelled from the property by pump K. The small area of low level vents provide background ventilation sufficient to remove radon from the basement room without creating cold drauhts. The cross-sectional area of vents is in line with current requirements of 8000mm per room. This 8000mm2 equates approximately to only a 10mm gap at the bottom of a standard internal door.

This low level purge ventilation is provided as part of a fan assisted balanced ventilation system that employs powered air movement components in supply and/or exhaust sides in order to achieve a design flow rate and ensure continuous extraction of radon from the low level room vents. The balanced ventilation system incorporates an automatic boost, linked to any extract fans in the property, to balance air flow when extract fans are used in kitchens and bathrooms so that negative pressure is always present at the room vents.

The system can be used with or without heat recovery.

The system can be used with cavity membranes and/or sheet membranes provided that the area behind the membranes can be depressurised.

This method can provide adequate ventilation that is both draught and pollution free.

It should be noted that a mechanical ventilation system can be used to reduce indoor radon concentrations because, if the system should fail, a short-term increase in indoor radon concentration is not a significant risk to the occupants (BRE, 1991).

De-pressurisation, using the above method, of the cavity at the rear of the plasterboard and/or vents into a room can also be used for removal of hazardous and land-fill gases.

Figure 4 shows the new method applied to a basement or ground floor room that has been constructed using sheet membranes M to walls and/or floors. There are instances where it is not possible to depressurise the area behind membranes, for example when sheet membranes are laid direct onto rock. The method is now applied to a building that does not have depressurised areas behind the membranes. The waterproof/radon membranes are a passive installation. However, the designer must now allow for defects and possible radon ingress.

This application now provides for collection of the radon that enters through defects in the passive membranes and also radon entering from higher rooms within the building. The radon pump K depressurises the area the area at the floor/wall join behind the skirting E. Radon is removed from behind skirting and plasterboard whilst also being extracted from the room via the vents provided. There can thus be no build up of radon at low level within the room.

Continuous negative pressure is maintained around the penmeter of the room by the use of small diameter connecting pipes N laid across door thresholds in floor screed G, the heavy gas will travel across the pipe towards the suction from pump K. The room vents are installed at low level, preferably low on the front face of the skirting to extract low lying gas within the room.

Figure 5 shows a cross section of a building that has only a sheet floor membrane M and is suffering radon ingress. The method can be applied using a radon pump K to create a depressurised area behind skirting and/or walls around the perimeter of the room. Again pipes set in screed across door thresholds will maintain negative pressure. The method in such a retro-fit application will handle radon ingress at the vulnerable floor/wall join and from behind plaster. It will also provide for removal of the radon that gains entry to the room itself by use of the low level vents between the room and the extraction area behind the skirting. In situations where the building is very leaky the radon ingress rate can be measured and extraction rates increased until radon ingress is reduced to acceptable levels. Yet again this low level purge ventilation is provided as part of a fan assisted balanced ventilation system that employs powered air movement components in supply and/or exhaust sides in order to achieve a design flow rate and ensure continuous extraction of radon from the low level room vents. The balanced ventilation system incorporates an automatic boost, linked to any extract fans in the property, to balance air flow when extract fans are used in kitchens and bathrooms so that negative pressure is always present at the room vents.

The system can be used with or without heat recovery.

The method described that removes radon from both structure and rooms of a building can be used in basements and any other rooms that suffer from radon ingress. In some instances rooms above ground also need radon protection. This method can be used in basement conversions and work to existing buildings.

This method can also be used in new build applications to ensure that where defects in membranes occur that design liability is satisfied as the method acts as a failsafe line of defence whereby the hazardous radon is actually physically removed from the rooms.

Claims (10)

1. Claims 1. A method of collecting gas that enters buildings and collects within rooms, the method comprising; -providing a depressurised area; and also -venting cavities and the room itself into the depressurised area.
2. 2. A method according to claim 1 where the depressurised area is introduced behind a floor and/or wall cavity membrane.
3. 3. A method according to preceding claims where the depressurised area is introduced behind a floor and/or wall sheet membrane.
4. 4. A method according to claim 1 where the depressurised area is introduced at the rear of a skirting board.
5. 5. A method according to previous claims that uses a sump as part of the depressurised area.
6. 6. A method according to preceding claims where the air and/or gas collected by the depressurisation from the structure and the rooms is exhausted clear of the property.
7. 7. A method according to preceding claims where the vents from the depressurised area into the room are at low level to collect heavy gas that collects in the lower area of the room.
8. 8. A method according to preceding claims to collect hazardous and land-fill gas.
9. 9. A method according to preceding claims that is part of a balanced ventilation system that employs air movement components in supply and/or exhaust sides in order to achieve a design flow rate and continuous extract at low level room vents. The balanced ventilation system incorporating automatic boost, linked to any extract fans in the property, to balance air flow when extract fans are used so that negative pressure is always present at the room vents.
10. 10. A method substantially as herein described above and illustrated in the accompanying drawings.Amendments to the claims have been filed as follows.Claims 142 1. A method of collecting gas that enters into a room of a building, the room is at least in part 143 below ground level comprising: (a) an above floor waterproofing system with a cavity membrane above the floor slab defining a cavity between the floor slab and the waterproofmg structure, and another cavity 146 membrane attached to at least one adjacent wall defining a cavity between the wall and the 147 waterproofing structure; 148 (b) a means of extracting gas from the cavities; and 149 (c) at least one means of connecting the interior of the room and the cavities.2. A method as in claim I in which a water drainage conduit is used to collect water as part of the 151 waterproofing system.152 3. A method as in previous claims where at least one part of the waterproofing system is of sheet 153 form.154 4. A method according to previous claims that uses an intermittent supply of air into the room in order to balance the air extracted by a intermittent fan such as the fans used in kitchens and 156 bathrooms in order to ensure that there is no blow-back or return of gas from the cavities into the 157 room.158 5. A method substantially as herein described above and illustrated in the accompanying 159 drawings.6. Apparatus substantially as herein described above and illustrated in the accompanying 161 drawings.