have agrement certificates .
to their sites are at the bottom of this page.
to Klober for this information.
STANDARDS BS 5250 1989:
Code of Practice for Control of Condensation in Buildings.
Moisture should be extracted at source to reduce the risk of water vapour
transfer from occupied areas of the roof. To achieve adequate cross
ventilation openings should, where possible, be placed on the longer
sides of a typical rectangular roof.
If ventilation openings are sited at intervals, they should be of equivalent
area to the continuous openings recommended, and avoid stagnant air
pockets due to inadequate through-flows. Opening sizes are minimum provisions,
with certain constructions there are advantages in increasing these
in order to ensure air movement through the roof void. Ensure that ventilation
openings cannot be blocked by dust, airborne debris, paint or frost,
and that the ingress of rain, snow, birds and large insects is prevented.
A nominal mesh size of 4mm is recommended, which would achieve this
and avoid excessive airflow resistance. Consideration should be given
to the use of proprietary ventilators where these will avoid problems,
or be more practicable in use. The ventilation openings should provide
a continuous weatherproof path from the roof void to the outside without
impairing the waterproof function of the structure, eg. the roof underlay,
vapour control layers or the roof covering.
For pitched roofs where ventilation at high level (eg. at or near the
ridge) is recommended, this is in addition to any low level requirement.
High level ventilation should never be used on its own as the suction
effect created will increase water vapour transfer into the roof void.
Thermal bridging should be minimised particularly at the external wall/ceiling
junction. and gaps in the ceiling should also be minimised and service
openings should be sealed. Where the insulation is at ceiling level
and where the eaves ventilation airway is provided between the insulation
and the sarking, they should be separated from one another by at least
Approved Document part F ‘Ventilation’ (revised 1995) states that:
‘Adequate provision shall be made to prevent excessive condensation
in a roof void above an insulated ceiling’. It also draws attention
to the BRE report ‘Thermal Insulation: Avoiding Risks’. This has been
prepared to give guidance to Approved Document part L - ‘Conservation
of Fuel and Power’. In particular it stresses the importance of: a)
Ventilating the roof space in accordance with BS 5250. b) Insulating
ventilation ducts in the roof space. c) Avoiding cold bridging by
carrying loft insulation over the wall plate and butting against the
wall insulation. d) Avoiding freezing of water in the tanks and pipes
by insulating pipe airflows and the top and sides of water tanks.
VENTILATION. AN EASY SOLUTION. The only practical way of preventing
condensation in the roof space is through effective ventilation. By
promoting cross currents of air, the entire roof void will be kept
well ventilated, dispersing any water vapour before it can condense.
To be effective, the ventilation has to be sufficient to cope with
the worst situation when moisture is produced - typically early morning
or evening, during spells of damp, cold weather when the air is still.
In recognition of the increased importance of controlling condensation,
both the Approved Document of the Building Regulations and the British
Standard relating to ventilation have been revised. A summary of the
main requirements which apply generally to all new and existing buildings
is given here, with specific situations tabled overleaf. It should
be noted, however, that anything differing markedly from typical domestic
situations may need special consideration. The Klober roof ventilation
products featured on the following pages have been specifically designed
to provide the most simple and cost-effective solution to condensation.
They can be used in new build, re-roofing and refurbishment situations,
and through their universal nature will simplify specifications and
is a symptom of modern living and of today’s preoccupation with saving
energy by minimising heat loss. The increased presence of central
heating, showers and modern domestic appliances produces greater amounts
of water vapour in the home.Even repiration gives of 1 litre of water
per person at night.A tumble dryer alone can give out over 6.5 litres
per day. Things get worse by the fact that these moisture-producing
activities are often concentrated at certain times of the day, followed
by long periods when the house is either unoccupied or unheated. In
addition, through greater draught proofing, double glazing and fewer
open fire places, ventilation is reduced throughout the home - encouraging
this moisture-laden air to rise into the roof space. Here too, natural
ventilation is virtually eliminated through the use of an underlay.
The traditional roof void is also cold because of the presence of
thicker insulation material. So as the warm, moisture-laden air rises
from below, it cools, reaches dewpoint, and condenses on cold surfaces.
If left unchecked, this condensation can cause severe damage to the
fabric of the building. Timber can rot, weakening the structure. Wetting
will cause timber and timber-based materials to swell and distort,
permanently damaging sarking boards and wall plates. Metal corrosion
can occur on components such as roof truss nail plates. Insulation
materials will absorb dripping water and lose their thermal effectiveness.
Ceilings could be damaged by condensation soaking through. Electrical
circuits could be affected. Mould growth will form, and anything stored
in the loft could be permanently damaged.
here is a brief description from Ruberoid
Performance Breather Membrane Rubershield-PRO is a three layer; highly
breathable waterproof membrane, constructed from high tensile spun-bonded
polypropylene layers, around a microporous polypropylene film.
outer layer forms the functional waterproof surface, the middle layer
is the breathable waterproof membrane, and the inner layer protects
the membrane from abrasion and damage, also giving additional strength.
This enables the fabric to allow moisture vapour to pass through,
whilst remaining fully waterproof.
Rubershield-PRO has a dark green upper surface, printed with the trade
name and head lap lines. Rubershield-PRO is a second-generation breather
membrane, conforming to the highest performance and professional standards.
Designed for use as a fully supported or unsupported breathable underlay
for tiled, slated or metal roofing systems, Rubershield-PRO is a triple
layer engineered fabric, ensuring full moisture vapour permeability,
whilst maintaining the highest levels of water resistance. The high
vapour permeability and waterproof nature of the membrane, combined
with excellent tensile/tear strength, make Rubershield-PRO the professional's
choice as the ultimate breather membrane. It is equally suitable whether
draped unsupported over rafters or laid directly over insulation.
Rubershield-PRO allows the escape of water vapour from within the
roof structure whilst protecting against wind driven rain, snow and
dust which may penetrate the main roof waterproofing, providing a
permanent quality breather underlay, which will last the life of the
BBA Certificate 01/3854 - (Warm roofs and cold ventilated roofs)
BRE Certificate 092/02 - (Cold unventilated roofs)
Breathable underlay for tiled and slated pitched roofs. For warm roofs
and cold roofs (ventilated and unventilated)