CONVERTING THE LOFT
Wood Campus Timber Trade Topics are produced in collaboration with the Timber Trade Federation. For further information, visit www.ttf.co.uk
TOPIC CHECKLIST
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Do I need planning permission?
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Do my plans meet Building Regulations?
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Do I need to consult a structural engineer?
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Have I checked for evidence of bats?
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Will I need to strengthen the joists?
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Am I installing a certified fire door?
Will I need planning permission?
The answer is YES if:
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The property is in a conservation area, world heritage site, national park or area of outstanding natural beauty
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The loft will be larger than 50m3 for a semidetached or detached home (40m3 for a terraced property)
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You plan to use materials with a different appearance from the rest of the property
Or if you plan to:
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Add a balcony, veranda or dormer window
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Change the height or pitch of the roof
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Or have the extension overhang the outer face of the wall of the original house.
This advice refers to houses. Check the Planning Portal for flats and other buildings. Contact your local planning authority if in any doubt.
Will I need Building Regulations approval?
Unless the conversion is for lightweight storage only and accessed by a retractable or removable ladder, the answer is YES.
The regulations will be applied to ensure, for example:
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the structural strength of the new floor is sufficient
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the stability of the structure (including the existing roof) is not endangered
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safe escape from fire
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safely designed stairs to the new floor
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reasonable sound insulation between the conversion and the rooms below
It is recommended that you contact Building Control to discuss your proposal and for further advice. You must also find out whether work you intend to carry out falls within The Party Wall etc. Act 1996.
Broadly speaking, interior cladding should be treated to Euroclass C-s3, d2. Refer to Approved Document B (fire safety) for details of fire safety requirements.
Never cut or remove any structural roof timbers such as rafters, purlins, struts or trussed-rafter components without the advice of a structural engineer.
Strength-graded timber
Any timber used for structural purposes must be strength-graded.
Strength-graded timber has a stamp, usually containing one of the following markings: C16, C24 or TR26.
Unmarked timber is unlikely to have been strength-graded and is not suitable for structural use.
Information on grade stamps for strength-graded timber is available in Timber Trade Topic no 4. Strength-grading.
Floor joists
Even if the loft was previously used for light storage, you will almost certainly have to strengthen the ceiling joists in the loft floor. You can do this by adding larger and stronger timber floor joists between the existing ceiling joists. Support them on the existing walls if they are strong enough, or add extra timber support beams if necessary. A professionally designed loft conversion plan that complies with building regulations will be needed. Check with a structural engineer.
Building regulations require 30-minute fire resistant floors for loft conversions in homes of two or more storeys.:
Load-bearing walls and foundations
New floor joists will need support. This can be achieved either from an existing wall, which will need to continue all the way down through the house to a foundation, or by an adequate intermediate support, such as steel or timber beams. It is particularly important to assess the structural integrity of older properties and houses with rooms knocked through on lower storeys.
In some cases, the proposed increase in load could require underpinning of the foundations. Check with a structural engineer or your building control body.
Bats
Bats and bat roosts are protected by law. If there are bats living in a roof, they cannot be disturbed or removed. If you see bats or bat droppings in the loft, you must notify the local Statutory Nature Conservation Organisation (see Further information and advice) to seek advice before work starts.
Getting your services in
There are rules about where and how much a structural timber member can be notched or drilled for wiring and pipework, as even a small amount of drilling or notching can weaken the timber significantly.
Holes or notches should not be cut in any rafters, purlins or engineered timber joists unless justified by the structural engineer.
Take advice from a structural engineer and your local building inspector.
Engineered products, such as I-joists may have drilling positions marked. Follow manufacturer’s instructions.
Photo: TwoTwenty Stairs
Stairs
Building Regulations apply, such as:
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A minimum headroom of 2m above a staircase, which means that the top of the stairs often needs to be close to where the roof is highest.
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In a multi-storey dwelling with a habitable loft where the stairs are the sole means of escape, the staircase must be constructed and enclosed so that it attains ‘protected stair’ status.
The main types of timber staircase you could use for a habitable loft conversion are conventional, spiral and alternating tread.
Retractable ladders are not acceptable for habitable rooms in the roof because they don’t provide constant access and means of escape.
Spiral stairs and alternating tread stairs are only allowed to access one habitable room (as well as a bathroom and/or toilet in the case of alternating tread stairs, as long as it isn’t the only toilet in the building).
The opening for new stairs is normally formed by cutting away some of the ceiling joists between the existing loft-space and the floor below. As these joists support the existing ceiling and restrain the pitched roof from spreading, you must provide replacement support, such as timber “trimmers” around the opening. These will probably be at least two timbers fixed together (double trimmer) to ensure the load is transferred to the remaining timbers.
Not all the guidance in the Building Regulations is compulsory for sound transmission, but you may need to comply with Approved Document E if any additional work is required to meet the standard in the existing property.
Bespoke staircases can be purchased from joinery manufacturers. Look for a member of the BWF Stair Scheme. Alternatively, timber components can be assembled on site. Download the BWF Stair Installation Guide.
Photo: Velux