Bedford School is an independent boys’ school catering for day pupils and boarders aged seven to eighteen. In 2001 Eric Parry Architects won a competition to design a new library at the school. The library has a curved brick upper storey with a barrel vault roof. A long window at ground floor looks out on playing fields.
Photo credit: Peter Cook
Architect: Eric Parry Architects
Structural Engineer: Adams Kara Taylor
Photo credit: Eric Parry Architects
Photo credit: Eric Parry Architects
Deep mass concrete strip foundations support load-bearing masonry ground floor walls and the beam-and-block ground fl oor itself. The external walls above fi rst fl oor level step out supported on a pre-cast concrete ledge element that transfers the load back to the ground floor blockwork. The first floor is a concrete slab cast directly onto the ledge counterbalancing the weight of the wall. Over the ground fl oor entrance and window the ledge is entirely supported from the mezzanine, which is in turn supported on concrete columns. The 215 mm brickwork wall wraps around the building in a continuous 56 m sweep with curved specials used to create the sinuous form. The whole-brick thickness and lime mortar specially tested by the BRE for strength allow movement joints to be eliminated.
Photo credit: Peter Cook
The roof is a barrel vault in section, extruded around the building to follow the curving perimeter wall. The wall was intended to carry the roof directly but the programme implications of allowing the lime mortar to fully cure before the roof could be started meant that steel posts had to be introduced to carry the primary roof steels. The roof and walls could then be built simultaneously. A series of curved universal beam (UB) sections form the vault, tied together with circular hollow section (CHS) purlins, some of which are curved twice in their length. Timber rafters are bolted to plates welded to the purlins. Each timber has been individually drawn and cut from a 250 x 50 mm joist to a unique curved profile. It was proposed to use a computer-controlled cutter but the contractor chose to cut each rafter by hand. The roof finish is pre-patinated zinc with single-ply membrane gutters and flat areas.
Photo credit: Peter Cook
Exploded diagram of roof structure
Site plan, scale 1:4000
Ground floor plan, scale 1:500
1. Foundations
2 m deep mass concrete footings.215 mm hollow blockwork wall slotted over reinforcement and fi lled with concrete.Mass concrete upstand.Liquid applied tanking membrane to all faces of concrete cill.Sheet bituminous tanking membrane to outer face of mass concrete.Sheet bituminous tanking membrane wrapped around beam ends and up to underside of timber cill.
2. Ground floor
17 mm reclaimed iroko boards glued to screed. 80 mm reinforced sand-cement screed over low temperature underfl oor heating pipes.30 mm rigid perimeter insulation.50 mm rigid insulation.Polythene vapour barrier.Beam and block fl oor structure.Ventilated cavity.
3. Mezzanine floor
Carpet fi nish.20 mm tongued & grooved chipboard.Underfl oor heating pipes with metal plate heat sink set into insulation.25 mm acoustic and thermal insulation.275 mm concrete slab.Painted plaster soffi t.
200 x 100 mm PFC (parallel fl ange channel) eaves tie beam providing restraint to external brickwork.200 x 200 mm SHS (square hollow section) posts bolted to mezzanine slab.
5. Mezzanine slab edge
Precast concrete structural ledge lintel.275 mm thick concrete mezzanine slab cast over ledge lintel.Flexible cavity tray over lintel.
6. External wall
215 mm class B wirecut facing brick outer leaf. Mortar 3:1 sharp sand:lime with no vertical movement joints.Cavity with 50 mm rigid insulation.Concrete blockwork inner leaf.Painted plaster fi nish.
7. Roof structure
Curved UBs (universal beam) with rigid plate connections to vertical SHS posts.Curved CHS (circular hollow section) purlins bolted to primary UBs.Mild steel plates welded to CHS.Curved timber joists cut from 250 x 50 C24 joists (max. 600 c/c) bolted to plates.
8. Parapet and gutter
PPC metal coping.Vertical single ply membrane to top of parapet. Single ply membrane gutter lining.WBP plywood gutter on softwood frame.Single ply membrane on softwood boards over vaulted area.
9. Ceiling
Three coats plaster on metal lath wired to bearers.12 mm diameter galvanised mild steel bearers suspended from joists on galvanised straps. Vapour barrier.125 mm mineral wool insulation.
10. Vaulted roof areas
0.7 mm standing seam pre-weathered zinc. 100 x 20 mm softwood boards 2-3 mm apart. 50 mm ventilation gap.High grade building paper roof underlay.
11. Stepped eaves
1 mm pre-weathered zinc eaves fascia. Insect mesh over ventilation slot. Single ply upstand.
12. Built-in seating
Painted MDF bench with slots over heater. Finned tube radiator curved to follow curve of window and seat.Skirting slot in seat for air inlet.
13. Window
Iroko frame with curved 12 mm toughened glass at corner.Concrete columns supporting mezzanine slab. In-situ reinforced concrete cill.Cobbles set in mortar to protect window and avoid need for manifestation.
External Wall Section
Post a Comment for "Bedford School Library"