Capit Building Products Limited - Tel: 01225 791124

CAPIT joist seals effectively limit air leakage and heat loss past the ends of built-in joists to assist in compliance with Part L and Part E of The Building Regulations.

High performance

Inexpensive

Quick and easy to fit

For all types of joists 

Click below to find out more ...

Product description Benefits More about Part L Product range Performance Data sheet Installation Pricing Stockists Contact Legal  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Product description

The CAPIT joist seal is an open-fronted and open-bottomed box that is injection-moulded in polypropylene.

It is fitted over the end of a joist that is to be built into a wall. The sides of the box converge slightly so that the seal grips the joist while the wall is built around it.

As the wall is built, a flange around the open front of the joist seal becomes embedded in the mortar to seal the CAPIT to the wall.

Once the wall has been built, the CAPIT joist seal is completely concealed behind the front face of the wall.

When used with a traditional timber joist which, in time, shrinks or splits, the CAPIT joist seal serves to limit air leakage through the wall .

When used with an engineered I-beam joist, the CAPIT joist seal blocks any air passageways that may remain between the web and flanges of the joist and the surrounding structure.

Benefits for house builders

Building regulation compliance:

CAPIT joist seals effectively assist in meeting the requirements of Parts E and L of the Building Regulations. They provide a better seal against air leakage than any other proprietary joist seal and better than flexible sealant. Click here for more information.

Health and safety:

CAPIT joist seals are used with joist ends built into the wall and avoid the risk of joist-hanger collapse.

Unlike other joist seals, once the joists have been laid and battened, with CAPIT joist seals there is no need to lift the end of the joist in order to fit the seal.

Unlike some other joist seals, CAPIT joist seals do not have large exposed flanges and tabs that cause a tripping hazard until the wall has been built around them.

Inexpensive:

CAPIT joist seals are competitively priced.

They avoid the costs of joist hangers, mastic and underslinging the floor.

Quick and easy:

The CAPIT joist seal simply fits over the end of the joist in a matter of a second or two once it has been laid - no need to lift the joist.

The CAPIT joist seal grips the end of the joist, while the wall is being built - no need for nails to hold it..

The wall is built around the capped joist end in the conventional way.

No need to wait for mortar to harden.

No exposed flanges to interfere with flooring or plasterwork.

Colour-coded for easy identification on site.

Strong:

The joist ends are supported directly on the wall.

No exposed flanges and tabs to impede proper tooling-in of the mortar all around the joist, front and back.

Compact:

Because of their design, CAPIT joist seals can be interleaved in their packaging, and they are devoid of large flanges and tabs to interfere with tight packing. It is estimated that a box of CAPIT joist seals occupies as little as about 15% of the volume of a box of the same number of flanged, closed-bottomed, joist seals. Less space taken up on site.

Versatile:

Each size of CAPIT joist seal:

fits any thickness of wall leaf over 85mm

can be trimmed on site for smaller joist heights

can be packed on site for smaller joist heights and thicknesses

can be used with traditional timber joists or modern engineered I-joists

and so a small product range covers all common joist sizes and types.

Simplified stocking, specifying  and ordering.

Greater use of left-overs.

Benefits for builders' merchants

Profitable: CAPIT is competitively-priced, superior product, and so there is no need to shave profit margins.

Compact: Because of their design, CAPIT joist seals can be interleaved in their packaging, and they are devoid of large flanges and tabs to interfere with tight packing. It is estimated that a box of CAPIT joist seals occupies as little as about 15% of the volume of a box of the same number of flanged, closed-bottomed, joist seals. Less space taken up in the warehouse.

Simplified stocking: Each size of CAPIT joist seal:

fits any thickness of wall leaf over 85mm

can be trimmed on site for smaller joist heights

can be packed on site for smaller joist heights and thicknesses

can be used with traditional timber joists or modern engineered I-joists

and so a small product range covers all common joist sizes and types.

Benefits for home owners

CAPIT joist seals assist in limiting unwanted air leakage though walls with built-in joists so as to:

reduce heat loss and thus reduce energy bills.

reduce sound transmission and thus sound pollution.

CAPIT joist seals enable the joist end to be built into the wall so as to reduce the springiness of the floor.

Unlike some other joist seals, CAPIT joist seals do not cause a reduction in strength of the wall around the joist end due to the impossibility of tooling in the mortar properly.

Benefits to the environment

CAPIT joist seals assist in limiting unwanted air leakage though walls with built-in joists so as to:

reduce heat loss and thus wasted energy resources.

reduce sound transmission and thus sound pollution.

CAPIT joist seals are, by comparison with some other joist seals, light in weight and simply manufactured so as to:

reduce material usage.

reduce energy consumption in manufacture.

CAPIT product range

CAPIT's small range of joist seals covers a wide variety of joist sizes and wall thicknesses.

Remember:-

Each CAPIT joist seal can be used with any wall thickness greater than 85 mm. There's no need for different seals for different wall thicknesses.

Each CAPIT joist seal can be trimmed in height to suit joists substantially smaller than 225 mm in height.

Each CAPIT joist seal can be packed when used with thinner joists.

Each CAPIT joist seal can be used with timber joists or engineered joists.

The figures speak for themselves

CAPIT is BBA approved - certificate No. 07/4459. To view a copy of the certificate in Acrobat format, click here.

NHBC accepts the use of the Capit Joist End Seal, when installed and used in accordance with the BBA certificate, as meeting the requirements of the NHBC Standards 2007, Chapter 6.1 External masonry walls, Design standards D12 and D13.

Tests carried out by CERAM on the CAPIT CY225/50 joist seal produced the outstandingly low leakage rate of 0.37 m3/hour at a pressure of 50 Pa.

According to Manthorpe's published data, corresponding tests carried out by CERAM produced values of 0.54 m3/hour for their joist seal; 0.59 m3/hour for a JHMI joist hanger; and 0.99 m3/hour for a joist end traditionally built into a wall with mastic detailing to NHBC specification.

According to Easy Joist's published data, corresponding tests carried out by CERAM revealed a leakage value of 0.57 m3/hour past their 225 x 45 mm joist cap.

PART L, JOIST-END LEAKAGE and THE CAPIT SOLUTION

Part L of the Building Regulations

Part L of the current Building Regulations and associated Approved Document L1A place tighter limits than before on the thermal insulation and air-tightness of new dwellings.

Limits are placed on:

the thermal conductivity ("U-values") of elements from which the dwelling is built,

the average U-values of the building’s walls, floor, roof, and door and window openings,

the measured air-tightness of the building envelope, and

the CO2 emission rate from the building.

Once built, dwellings need to be pressure tested to determine their air-tightness. If the measured value is outside the limit, remedial measures need to be taken.

The CO2 emission rate is calculated to provide an improvement on the CO2 emission rate of a notional dwelling having the same size and shape and constructed according to particular reference values that were current in 2005. Currently, the required improvement is 20%. In time, a greater improvement will be required; the Government’s aim is to achieve a reduction in CO2 emissions of 60% by the year 2050.

The calculation of the CO2 emission rate depends on the air-tightness of the building envelope. During design, a value for the air-tightness can be assumed. However, once built, the CO2 emission rate needs to be recalculated to take account of the actual air-tightness measured by the pressure test and also any changes in design made during construction. If the CO2 emission rate, as constructed, is outside the limit, then again remedial measures need to be taken

During a transitional period until October 2007, the remedial measures merely needed to improve the situation in prescribed ways. However, since November 2007, it has been necessary to remedy the situation completely.

In most cases, remedial work will be difficult, expensive and time consuming. It is therefore imperative, during the design and construction of a dwelling, to take all possible steps to reduce air leakage.

In summary, a leaky dwelling may fail to comply (a) simply because it is not sufficiently air-tight, or (b) because the CO2 emission rate as a result of the leakage is too high. Reducing air leakage can therefore assist with regulation compliance on two fronts.

Joist End Leakage

Joist ends can either be built into the supporting wall or be hung on joist hangers. Due to the risk of floor collapse during construction (see for example HSE warning, 29 January 2007), it is preferable to build joist ends into the supporting wall, rather than hang them on joist hangers. However, a joist end built into the internal leaf of an external wall can result in significant air leakage due to:

an insufficient initial seal between the joist end and surrounding mortar,

shrinkage or splitting of the joist,

shrinkage of the mortar and

flexing of the joist end in the wall with varying loads on the floor.

To reduce the leakage, Accredited Details MCI-IF-02 (version 1.0) (page 5) states that "mortar joints around built-in joists should be recessed or struck and carefully pointed with flexible sealant." Air leakage tests carried out by CERAM show that the air leakage past a joist end sealed in this manner is 0.99 m3/hour (at 50 Pa). It will be appreciated that the application of flexible sealant entails an additional time-consuming step in the construction process, after the wall has been built around the joist ends and before the floor is laid on the joists.

The Accredited Details go on to say that, alternatively, joists may be fitted with proprietary shoes as they are installed. A few proprietary joist shoes are now available on the market.

Which Joist Seal?

In order to achieve low air leakage, a joist shoe needs to:

facilitate a good initial seal between the joist shoe and the surrounding mortar, and

maintain that seal despite:

shrinkage or splitting of the joist end,

shrinkage of the mortar, and

flexing of the joist end in the wall with varying loads on the floor.

There is only one joist shoe on the market that satisfies all of these requirements, the CAPIT joist seal A from Capit Building Products Limited.

The CAPIT joist seal is a plastics box with an open bottom B which is simply slipped over the end of the joist c at any time before the wall is built up around the joist end, and which has a 10 mm flange d around its sides and top which becomes embedded in the mortar part-way through the thickness of the wall as the wall is built up.

Unlike other joist seals, the CAPIT joist seal does not have any large exposed flanges efg that impede the proper tooling-in H of the mortar around the joist and joist seal. Therefore a good seal can initially be achieved without the use of any additional flimsy foam rubber sealing J or flexible sealant.

Unlike other joist seals, the CAPIT joist seal’s small flange d is embedded in the mortar and maintains the seal despite any shrinkage of the mortar.

How effective is CAPIT?

Tests carried out by CERAM showed that the air leakage past a joist end sealed with a CAPIT joist seal was 0.37 m3/hour (at 50 Pa). That amounts to a reduction of 63% compared the figure of 0.99 m3/hour for a joist sealed with flexible sealant and is 32% better than any of the published leakage figures known to us for the other proprietary joist seals.

For a typical dwelling having, say, fifty joist ends built into external walls, the total reduction in air leakage by using CAPIT rather than flexible sealant therefore amounts to over 30 m3/hour (at 50 Pa).

That reduction in air leakage enables a looser tolerance to be employed for other leaky areas of the envelope, and could make the difference between compliance with the regulations, or non-compliance and expensive remedial work.