1. what’s so good about loft conversions? · pdf filewhat’s so good about loft...
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LOFT CONVERSIONS Ian Rock MRICS
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1. What’s so good about loft conversions? 2. What’s new? - Legislation 3. Key design options 4. What Type of Roof ? 5. Complying with Fire 6. Loft stairs 7. Designing the new structure 8. Loft windows 9. Loft confusion 10. Surveying lofts 11. Case Study Based on the Haynes Home Extension Manual
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1. What’s so good about loft conversions? According to research from Nationwide Building Society loft conversions are the single most valuable home improvement:- Average % value added 1. Loft conversion + 21% 2. Another bedroom + 12% 3. Central heating + 6.8% 4. Parking + 6.5% 5. An extra bathroom + 5.2% Loft conversions also give you ‘more space for your money’ Typical costs Basement conversion (50m2) £ 70 - £100,000 Home extension £ 25 – 60,000 Loft conversion £ 15 - 35,000 Conservatory £ 8 - 15,000 Converting integral garage £ 6 – 15,000 Converting outbuildings £ 5 – 15,000 Removing internal walls £ 1 – 5,000 BUT not all roofs can be successfully, or easily, converted.
AND there are many examples of poor quality loft conversions. Large box (mainly pre- 1988) dormers can detract from historic townscapes.
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2. Legislation PPllaannnniinngg nneeww rruulleess ffrroomm OOccttoobbeerr 22000088 •Conversion of roof space to living accommodation is generally permitted if there is not a change to the plane of the roof fronting a highway (beware of corner sites!). •It must not exceed the height of the original roof. •It must not increase the volume of a terraced house by more than 40 cu. m. or 50 cu m. in other cases. Specifically - to count as ‘Permitted Development’:- •Dormers: must be set back at least 200mm from the eaves, as far as practicable. •Materials: should be similar in appearance to the existing house. •No balconies, verandas or raised platforms – including roof windows with ‘fold-out balconies’ •Windows: side-facing windows to be obscure-glazed and non-opening unless the parts that can be opened are more than 1.7m above the floor of the room.
The Building Regs from April 2007 - Key Changes to the Approved Documents
* Escape from fire should be via a protected corridor / stairway (min 30 mins fire resistance) leading out to an external door. * Where open-plan room layouts exist at ground level, a new partition will be needed to enclose this escape route (or possible sprinkler protection + fire door) * Emergency escape windows now not essential (for floors over 4.5m above ground) * Fire doors are now required to the protected escape path * Self- closers no longer required
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3. Key Design Options Questions to ask - at the design stage - How much headroom is there in your existing loft? - Do you plan to install a large box dormer, traditional small dormers or just rooflight windows? - How will the new floor joists be supported? - What roof support is required at purlin & ridge level? - How many new steels / beams will be required? - Location of loft stairs? - Fire implications to the whole property? DORMERS * Large dormers – type: full width, large box or mansard?
* Small ‘cottage’ dormers: There’s a wide variety of traditional dormer and ‘half-dormer’ styles. Although they look good externally, they don’t add much space internally.
SKYLIGHTS There’s also a wide variety of roof windows – not necessarily Velux !
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4. What Type of Roof ? i. Traditional cut timber
Rafters, purlins, struts or collars. Rafters spaced about every 400mm
ii. The TDA roof - Timber Development Association - Post war to c. 1960s
Bolted trusses spaced about every 1.8m (typically 3 per roof)
iii. Prefabricated trussed rafters (post c. 1965)
Trusses typically spaced at 600mm centres iv. Contemporary ‘Room In Roof’ attic truss
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5. Complying with Fire Typical 2 storey to 3 storey conversion, with loft floor more than 4.5m above external ground, but less than 7.5m. Compliance is more arduous for conversions above 7.5m where sprinkler systems and external fire exits may be required.
Properties with conventional hallway and stairs These double as escape corridor - as long as you fit fire doors to habitable rooms. Properties without entrance halls Either construct a new partition wall to form a new hall leading to main exit door OR provide choice of escape routes via rooms to final exit doors - and fit fire doors. 6. Loft stairs Building Regs offer some useful concessions for stairs to loft rooms
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Where there’s not enough space to achieve 2m headroom, reduced headroom can be acceptable. Alternating tread ‘paddle’ stairs or a fixed ladder may be acceptable as a single flight + handrails both sides. Or spiral stairs, but only OK to a single loft room. 7. Designing the new structure There are 3 main levels where new beams may be need ed - FLOORS A pair of new beams are installed across the ceiling joists, about ¼ distance in from front and rear. Supported in side walls. - PURLINS When you remove the old purlins (or their struts), bang goes their support! Adding new steel or manufactured timber purlins is one way of compensating. - RIDGE Normally required to support large dormer flat roof joists and to strengthen the existing ridge.
Getting around the problem of chimney breasts New Floor joists - DIRECT support from internal walls Only suitable for some older properties. Main walls and spine must be able to support new loadings - INDIRECT support from new beams Normally from one side wall or party wall to the other
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Positioning the new joists – Options:- 1. Overslinging New floor joists run above existing ceiling structure (where headroom isn’t an issue). Ends of the new floor joists slot into the side web of new beams. 2. Side-slinging (‘underslinging’) New floor joists run alongside existing ceiling joists. Their ends hang down below new support beams, e.g. from long legged joist hangers. 3. Ceiling to floor conversions New beams run under old ceiling allowing it to act as new floor – where headroom below permits. 4. Dropped ceilings Demolish the old ceiling and build new floor/ceiling underneath – where head room below permits.
An interesting new alternative
Extendable lightweight aluminium beams slide into roof space by removing just three rows of tiles on one side of the house Minimises disruption – no need for heavy steels LABC approved system, minimising loss of headroom Spans up to 8.4m Primarily for trussed rafter roofs
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8. Loft windows
Escape windows are no longer relied on as an escape route (for floors over 4.5m). To count as an ‘escape window’ a window must have a minimum clear opening of 0.33 sq m, with a minimum 450mm width and height). Escape windows on roofs need to be set back with a max distance to the roof edge of 1.7m (sill to eaves). Potential conflict between child safety and ease of escape, therefore sills should be no higher than 1.1m above floor level, but no lower than 600m (skylights) or 800mm (dormers). However ‘Juliet balconies’ with balustrades and French windows are fairly common. The distance between dormer window sills and the existing roof should not normally exceed 225mm.
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9. Loft confusion Comparing 3 quotes – are you comparing like with like? Example:- Basic comparison QUOTE 1 QUOTE 2 QUOTE 3
‘Full width dormer’
London stock brick cheeks
1 bedroom 1 e/s shower/WC room
to rear
‘dormer style’ conversion eternit 2000 ‘slate tile’ hung
2 bedrooms
1 e/s shower/WC room to rear
‘15ft width dormer
Tile hung’
1 bedroom 1 e/s shower/WC room
to front
Planning Permitted development
assumed Permitted development
assumed
Permitted development assumed
Drawings YES YES YES imperial measurements! Structural engineer’s calculations
YES YES YES
Building Control fees included?
NO ? ?
‘ a LA completion certificate will be obtained and given to
you on completion’.
? ’all work necessary to comply with B. Regs’
All liaison with Council
YES ? ?
Timescales ? ? 10 – 12 weeks Supply & remove all scaffolding
Assumed YES YES Assumed YES
Supply sanitary fittings Shower, WC, basin, taps etc
NO NO YES
Decoration included
NO NO NO
PRICE NET £
35,620.00
PRICE inc VAT £
30,995. 00
41,853. 50
33,500. 00
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Detailed comparison PRICE inc VAT
£
30,995.00
41,853.50
33,500.00
Adjustments
Less £ 8,225.00 inc VAT without extra bedroom to rear
addition
= £ 33,628.50
+ fire doors
ADD £ 1400 inc VAT *
= £ 34,900.00
E X T R A S
Dormer windows included Optional French windows
‘double glazed made of wood’
ADD + £ 980.
UPVC windows
Not offered
UPVC windows
Not offered
Sanitary fittings & shower
ADD approx £ 850 ADD approx £ 850 INCLUDED
Fire doors to replace existing doors in house
INCLUDED INCLUDED NOT INCLUDED *
Decoration
ADD £ ADD £ ADD £
B Regs fee
Not included ADD £ 500
assumed not included ADD £ 500
assumed not included ADD £ 500
Tiling to bathroom shower etc
ADD £ ADD £ ADD £
Laminate flooring or carpet over bare chipboard
ADD £ ADD £ ADD £
Any necessary upgrading to existing CH & electrics
ADD £ ADD £ ADD £
Blinds for roof windows
INCLUDED ADD £ ADD £
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10. Surveying lofts How should clients be advised where works do not comply with current Building Regs? What’s acceptable and what isn’t? Q. Is it an original attic, or is it a conversion ? Clues in period properties include lathe & plaster to rafters, and old gable windows. Q. Did the work require consent when it was carri ed out? If so, what were the rules at the time of construction? e.g. open plan ground floor layouts? original doors to habitable rooms? Q. Was consent obtained? A completion certificate not just a ‘plans approved’ document. If not, advise a regularisation application (but likely effect on valuation?) Q. Does it comply with current regs? (especially structure & fire safety) Probably not – but is any non-compliance significant for the client?
CONVERSION COMPLAINTS The 2 most common customer complaints about new loft conversions are:- 1. Ceilings too low 2. Too hot in summer OTHER ISSUES Large dormers
* Quality of coverings? * Access for maintenance? * Insulation ?
Openings for dormers and roof windows - are the rafters doubled up and trimmed?
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11. Case Study
Converting a modern trussed rafter loft
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Steel ‘purlins’ 203 x 133mm UB30 on padstones each end.
New 38 x 195mm C24 floor joists (span 4.8m) are installed below the existing ceiling joists (to gain headroom above).
‘Preserving the triangulation’
New floor joists connected to existing 38 x 70mm timbers using ‘Strong Tie’ camplate / nailed plates. New timber stud ladder walls constructed on top of steel purlins to rafters, 50 x 100mm timbers.
New floor joists use 38 x 195 C24 @ 600 centres, from long leg adjustable support hangers.
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Existing rafters doubled up from ridge to new purlin wall with 50 x 100 timbers. New 50 x 100 collars bolted to rafters before cutting the original structure!
Roof windows Skylights fitted from above (some designs can be installed from within roof space). But which trade – roofer or carpenter?
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Insulation – complying with Part L ELEMENT PRODUCT / DESCRIPTION
U-Value
Kingspan phenolic foam
RAFTERS K 7 70mm insulation between rafters
0.2
K 18 62.5mm insulated plasterboard under rafters (50mm +12.5mm)
GABLE END WALL cavity blockwork
K18 62.5mm insulated plasterboard (50mm +12.5mm) To blockwork or to remaining timber truss
0.3
CEILING K 7 100mm insulation between joists K 18 37.5mm insulated plasterboard under joists
(25mm +12.5mm)
0.2
K12 80mm insulation between studwork STUD WALLS (excl. eaves cupbd doors)
K18 37.5mm insulated plasterboard on top studwork (25mm +12.5mm)
0.3
TIMBER FLOOR
K 3 100mm insulation between joists 0.23