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Why Ventilate Roofs?
Roof ventilation is to avoid condensation.
- Condensation has only become a problem in buildings
over the last twenty years or so. It was not a problem
with
‘traditional’ building methods and materials,
which were less airtight than they are today resulting
in plenty of ‘natural’
ventilation,which gave relatively poor levels of insulation.
- Nowadays everyone expects a warm draught-free home
with low energy costs, and the requirements of the
Building Regulations
ensure this. Necessary increases in thermal insulation,
more heat, and less draughts and air movement, lead
to an increased
risk of condensation. As expectations rise, the risk
increases. Building Regulations Part L1 came into
force in April 2002, they
specify more ceiling insulation, with U-values down
to 0.16 W/m2K.Condensation risks will rise in proportion.
Product Brochure
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Product Range
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Corovent Dry Fix |
Corovent Universal Dry Fix Verge System
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Designed to provide a simple, secure method of mechanically fixing verge tiles. Reduces the risk of wind damage and water penetration.
- EFVB-LH & EFVB-RH:- Dry Verge Brown Left Hand/ Right Hand
- RCB-A:- Ridge Cap Brown Angled
- RCB-HR:- Ridge Cap Brown Half Round
- SP-B:- Starter Piece Brown
- EFVG-LH & EFVG-RH:- Dry Verge Grey Left Hand/ Right Hand
- RCG-A:- Ridge Cap Grey Angled
- RCG-HR:- Ridge Cap Grey Half Round
- SP-G:- Starter Piece Grey
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Corovent Universal Dry Fix Ridge System
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Dry fix ridge systems speed on-site installation . They eliminate the need to carry mortar to the top of the roof making ridge installation easier, quicker and safer.
- URS6:- 6m Universal Dry Fix Ridge System
- URS6/RT:- 6m Roll-Out Tray
- URS6/US:- Dry Fix Ridge Union Strap
- URS6/RC:- Dry Fix Ridge Cap
- URS6/BK:- Dry Fix Ridge Bracket Kit
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ARIEL offers a complete solution to all roof condensation risks. ARIEL products meet all the requirements of Building Regulations, British Standards and NHBC. Products include cowl vents, roofline vents, ridge vents, and all types of eaves vents, for all slate and tile roofs. Pipe vents include soil pipes, and all ‘wet’ room vents (eg kitchen and bathroom). All offer the ARIEL colour and texture matching service, making them almost invisible from ground level. The roofing accessory range also includes the best valley troughs on the market.
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COROVENTS comply with all British Standard
requirements and N.H.B.C. regulations. |
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| For
Roof Space Ventilation Refer to: |
| Building Regulations Approved Document
F2: 1995 ‘Condensation in Roofs’ and subsequent
amendments. |
| Building Standards (Scotland) Regulations
1990 Part G. (where applicable) |
| BS5250:1989 ‘Control of Condensation
in Buildings’ |
| BS5534:PT1:1990 ‘Slating and tiling
design’ |
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| For
Soil Vent Application Refer to: |
| Building Regulations Approved Document
H1 1990 ‘Sanitary pipework and drainage’ and
subsequent amendments. |
| BS5572:1994 ‘Code of Practice for
Sanitary Pipe work’ |
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| For
Passive Stack VentilationRefer to: |
| BS5925:1991 (1995) ‘Code of Practice
for ventilation principles and designing for natural ventilation’ |
| Building Regulations : Approved document
F1 1995 ‘Means of Ventilation’ |
| BRE Information paper 13/94 ‘Passive
Stack Ventilation systems: design and installation’ |
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| For
Mechanical Ventilation Refer to: |
| Building Regulations Approved Document
F1 1995 ‘Means of Ventilation’and subsequent
amendments. |
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| For Futher Guidance
Refer to: |
| NFRC Technical Bulletin No.20 ‘Roof
ventilation products’ |
| Approved Document F2 (1995) Building Regulations
and BS5250:1989 ‘Control of Condensation in
Buildings’ describes the causes, problems, and
practical methods for avoiding condensation. Here
are the key points of these requirements:
Condensation
The requirement of Approved Document F2 is that condensation
is reduced in order that it will not cause damage
to the structural or thermal properties of materials
in a roof. Dampness is caused by: weather, interstitial
condensation, surface condensation, and construction
water (in wet constructions).
Ventilation
Ventilation is necessary to avoid the problem of
condensation. Adequate cross ventilation is required,with
openings placed on the longer sides of a typical rectangular
roof. This eaves to eaves
ventilationrelies on wind power. In most cases the
ventilation system is improved by utilising the natural
thermalupflow of air in a roof void. This eaves
to ridge ventilation also avoids the problem
of stagnant air pockets due to inadequate through-flows.
Warning: high level
ventilation should never be used on its own as the
suction effect created could increase water vapour
transfer into the roof void.
Ventilation should provide a continuous weatherproof
path from roof void to the outside. Openings must
not be blocked by dust or debris, and ingress of rain,
snow, birds and large insects must be prevented. Mesh
size of 4mm is recommended by BS5250, it is small
enough to prevent entry by nesting insects, birds
etc. yet is large enough to prevent blockage, provide
adequate air movement and avoid excessive airflow
restraint. Ventilation is recommended in all circumstances.
NRFC bulletin 20 states: ‘any water vapour transmission
benefit of a vapour permeable roofing underlay cannot
on its own eliminate roof space condensation. Any
water vapour transmission benefit should be treated
as fortuitous.’ Where a vapour permeable underlay
is used, it should therefore be in addition to, rather
than in place of, ventilation of the roof void. Ventilation
openings can be sited at intervals, they should be
of equivalent area to a continuous opening:
5mm air gap = 5,000mm 2 /m ventilation
10mm air gap = 10,000mm 2 /m ventilation
25mm air gap = 25,000mm 2 /m ventilation
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| Open Roof
Void |
Building
Regulations state: where the void is open, eaves
to eaves air flow is effective, along the longer
sides of the building. Ariel recommend the use
of high level ventilation in addition to eaves
ventilation in all cases - as it utilises the
natural thermal uplift in a roof void. Eaves
to eaves ventilation relies on the wind conditions
which can result in poor through flow and stagnant
air pockets.
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PITCH 15° or less
Use: eaves vents |
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PITCH 15°or greater
Use: eaves vents Or: low level slate/tile vents |
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| Or: low
level slate/tile vents 25mm air gap |
10mm air gap In addition
BS5534 recommend: Use: ridge vents Or:high level
slate/tile vents 5mm air gap. |
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| Steep
or Wide Buildings |
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to eaves vents, increased ventilation must be
provided by high level openings. These are necessary
to avoid stagnant air pockets due to inadequate
through flow. In particular for roof slopes steeper
than 350, or for buildings more than 10 metres
wide, high level ventilation is required. |
PITCH
35°or greater Or: WIDTH 10m or more,Use:
eaves vents Or :low level slate/tile vent
25mm air gap&: ridge vent 5mm air gap Or:
high level slate&tile vents 5mm air gap
each side.
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| Single
Pitch Roofs |
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PITCH 15°or
less
Use: eaves vents
Or: low level slate/tile vents25mm air gap&:
highlevel slate/tilevents 5mm air gap Use:
rafter trays10mm/25mm
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PITCH 15°or greater
Use: eaves vents Or: low level slate/tile
vents10mm air gap& : high level slate/tile
vents5mm air gap. |
Where eaves ventilation is
provided care should be taken to prevent
insulation blocking off air flow to roof.Use
ventilation at the eaves and at the abutment.
PITCH 15°or greater Use: eaves vents
PITCH 15°or less Use: eaves vents.
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| Pitched
Roof - Ceiling & Insulation Inclined
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Where the insulation
follows the line of the roof, it is necessary
to ventilate both at low and high levels.
An air gap of at least 50mm must be maintained
between the underlay and insulation all
the way along the inside of the roof in
order to prevent air resistance in this
area. Where joists run at right angles to
the air flow, use counter battens.
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| Insulation follows
line of attic room. |
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Insulation follows line of
roof. |
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Air flow between
Roofing Underlay and Insulation: eaves vents
OR: low level slate/tile vents 25mm AND:
ridge vent 5mm OR : high level slate / tile
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| Pitched
Roof - Obstruction in Roof |
All isolated parts of the
roof should have ventilation provision.
Where an obstruction in the ventilation
path occurs, such as at roof lights or at
changes in pitch, the roof void should have
additional ventilation openings.
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Obstruction outside inclined
ceiling.Immediately below the obstruction
5mm Immediately above the obstruction
25mm |
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Obstruction within inclined
ceiling.Immediately below the obstruction
5mm
Immediately above the obstruction 10mm
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| Pitched
Roof - Dormers |
| Pitched type dormer roofs
should be ventilated from eaves to eaves.
Flat type dormer roofs should be ventilated
from eaves to ridge of the main roof. |
Pitched Type Dormer,
USE: eaves vents OR:low level slate/tile
vents 10mm |
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Flat type Dormer, USE: eaves
vents 25mm |
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Main Roof : ridge line 5mm
Or : high level slate / tile vents 5mm each
side And: eaves vents / low level slate/tile
vents 25mm.
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