Repairs: roofs and rainwater goods

Problem 9: Over-stressed or broken hip boards

Where a hipped roof has been re-covered, the hip board may well be over-stressed from the increased load. It is likely to buckle, or bend or sometimes snap, because the hip board is usually slender in comparison to the rafter thickness.

Solution

The hip can often be propped and the prop supported in turn on a ‘dragon beam’ run across the corner of the building. The beam needs to be stiff enough not to bend under the point load imposed by the prop, and needs to be fixed securely so it will not shift under the load or any accidental impact.

Ideally the beam should also be lifted a little above the top of the existing ceiling joists so that if it were to deflect it would be unlikely to press down onto the existing joists.

Consider also Problem 7, Solution 3.

Note: Watch out for ceiling joists, which once restrained the rafters at the end fixings but now do not. A hundred years since the roof was constructed, old fixing nails are likely to have rusted away, amply assisted by shock from wind loads or, in some cases, wartime bomb damage.

Beware of bomb-shock damage

Where bomb shockwave has occurred, observe how often the joist overlap at the centre of the building is now gapped or buckled. Occasionally the entire roof frame is displaced across the building by 50mm or so.

The local library or the local authority’s Building Control Department often retain a copy of the war damage record, which can be checked if there is a suspicion that damage of this nature has occurred.

These records were originally maintained to plot valid claims for war damage compensation, but some of those repairs were by necessity of a very immediate nature with building materials in short supply during and immediately after the war, and they may bear careful re-examination.

It can help rule out (or in) damage from other causes such as subsidence or structural failure of the roof frame.

A check of the fixings at rafter feet and ceiling joists and at ceiling joist laps could enable a very cheap, but cost effective, screw fix repair at these nodal points. Note: check the joists where they lap in the centre of the roof – not just the fixings at the eaves.

Roof hip plywood dragon beam variation in plan

Ply gusset for hipboard repair

Roof spread and 'collar' repairs

COST SEQUENCE - Repair to broken hip board

  1. Cut pair of plywood webs/gussets to fit triangle of roof space.
  2. This repair is only likely to be suitable for repairs to hip boards up to about 2m in length.
  3. Longer lengths will need to be fabricated with built up panels of plywood of sufficient size to be brought through the roof access hatch.
  4. Allow for nominally a 2m run length along the hip board with corresponding right-angled triangles to lower edge and internal edge of web.
  5. Cut sockets so that the ply webs can be slid under the existing rafter locations.
  6. Construct timber binder in nominally 200mm by 50mm section timber spanning from the hip board location to internal load bearing wall if within suitable span, or construct T-beam with hanger spanning from internal/party wall through to adjoining main wall. Add vertical prop in 50mm section timber to close the inner edge of the ply gusset/sandwich. Slide over defective hip board and allow for stud bolting or screw fixing in shear resistant quality screws at nominally 300mm centres.

Repair to broken hip board - COST £300

Small works pricing

Since the original price estimating in 2008 the economic turmoil of the last few years has caused some disparities in pricing - if you are reviewing these figures in the London area they may look laughable - if you are located in Hull they might still look a bit expensive. Please treat them with caution and of course always consider obtaining more than one quote against which to test prices. Reference to the BCIS or a small works pricing book such as Spons or Laxton's will help assess costs and the hourly labour rates upon which they are based.