Roof Truss replacement costs
Roof repairs and maintenance are a fact of life and a well cared for roof will keep you warm and dry for decades. However, sometimes, you may take on a property where the roof is coming towards the end of its life or requires more extensive repairs; this could be caused by the penetration of water and damp or by storm damage. The roof trusses may need replacing to make the property safe again. Roof truss replacement costs would not be more than £250-£500 for a single truss, however, it's best to speak to a local roofer to get a more accurate cost.
Last Updated: October 2022
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What is a roof truss?
A roof truss is part or all of the wooden framework which supports a roof, other terms which are used interchangeably to refer to this are roof joists and rafters. Collectively they form the triangular wooden structure which supports the roofing material.
Roof trusses are the upright sections of wood which usually occur at regular intervals, their size and spacing to some degree dictated by the weight of the roof above them. They are linked by longitudinal timbers called purlins. The space between each truss is referred to as a bay.
Why would you need to replace a roof truss?
Sometimes damage can occur usually linked to extreme weather events such as storms or high winds. A falling tree can irreparably damage a roof truss which will mean it needs replacing. The other most common cause of damage to roof trusses is the ingress of water which normally takes place over a period of time and remains sometimes hidden to the householder. This is more typical in older or period properties where the end of the trusses sit either on or in the supporting walls and are therefore much more vulnerable to damp.
Occasionally roof trusses begin to struggle because they are just carrying too much weight so a roofing material that is too heavy for the size, grade and specification of the timber. It is always important when you are replacing roofing material that you choose a tile or slate which the trusses can support. This problem is sometimes evident when the roof starts to sag although this can also be caused by rot due to water leaks and penetration.
What is the cost for replacement?
Price varies depending on the type of timber and the size and specification of the wood but a single truss would not be more than £300-£400. Where the cost comes in however is putting that truss in place so there will be scaffolding hire to access and strip off the roofing materials plus usually a crane is required to lower the beam into place. So it would cost at least double again to fit it. For replacing more than one truss, it would be more economic to consider a completely new roof where all of the trusses were manufactured off-site and lowered into place as a complete unit.
Can you repair a roof truss?
You can repair a roof truss or joist and the feasibility of repair will depend on the extent of the rot and how many trusses are affected. Working on a cost of £250-£500 per joist, the bill can quickly add up.
The truss is repaired by cutting out the rotten wood and then splicing in a new fresh section of timber which is secured to the original joist by either high tensile steel rods or metal plates. If rods are used, then the new timber is hollowed out effectively to accommodate the rods and then the cavity filled with wood resin. The truss will need to be propped whilst the work is undertaken and it may involve removing floorboards or the loft boards.
Which is better, repair or replace?
This decision is usually governed by the extent of the repair work needed and what the final bill might look like. Sometimes a new roof is the better economic option particularly if there are other problems with the roof which need remedying in addition to the roof trusses. Don’t forget that you won’t just be paying for the repair to the affected trusses; you will also need to find the source of the problem and fix that as well. There is no point repairing or replacing roof joists if water continues to penetrate. A new roof costs in the region of £4,000-£8,000 and if your repair bill is coming close to the lower end of this range then it might be time to consider a new roof in its entirety.
Do you need planning permission to change roof trusses?
You will only need planning consents if your property is listed or within a conservation area. The only thing that could interest the planning authorities on an unlisted house in a normal residential area is if you change the height or pitch of the roof or add dormer windows which project beyond a specified distance from the roof plane; both of these scenarios will require planning permission.
If you are just repairing trusses then you should not require planning permission but if the house is listed then you can check that with the local planning authority or Historic England. It may be necessary to use certain procedures or materials commensurate with the age of the house.
How to find a roofing contractor
If you need work done to roof trusses then shop around for two or three quotes before choosing your roofing contractor. You will need a thorough site inspection as it may well be that if one truss is rotten that it is spread to others. You won’t receive an accurate quotation without a proper survey as there are bound to be other problems which then come to light and impact on the overall bill.
Roof trusses are essential to the integrity and safety of your roof which will not be weatherproof and watertight otherwise. However small targeted repairs can be effective. Your roofing contractor can advise you whether repairs or complete replacement is the better option. Maintaining the integrity of roof trusses is very important as without this, the whole roof will become structurally unsound and will end up both potentially unsafe and not weatherproof. Water will eventually penetrate through the roof void into the upstairs rooms below causing damage to plasterwork and internal decoration.
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