Roofing problem in survey

TrickyDicky

We've had this come up in our homebuyers report:

Softwood timber gang nailed trussed rafter construction with tiles laid to under felted timber battens.

Significant condensation problem within roof void. I would suggest static ventilation is provided by air bricks to gable end and preferably under soffits. Timbers are damp/wet. Condition rating 3.

Diagonal and horizontal cross bracing has been upgraded but not to a high standard. Ideally recommend upgrading. Condition rating 2.

Sarking felt is torn to front roof void area. Condition rating 2.

Is this kind of problem likely to require a huge refurb, or are air bricks easily installed be a decent roofer?

silvercar

Installing airbricks is just a question of hammering out the old brick and shoving in the new airbrick, bit of cement to secure and job done. Apart from the lack of ventilation is there another problem? It could just be that with poor insulation the roof viod is as warm as the rest of the house and the outside is cold, causing condensation. If this is so, then loft insulation would reduce your heating bills and help reduce condensation.

TrickyDicky

Was just condensation. Also identified the water tank not having a lid on which was probably making the problem worse.

There was a slight condensation problem in the rest of the house too, but this wont be helped by lack of extractor in the kitchen and bathroom.And the current owners may not be leaving a window open.

David_Aldred

Hi Trickydicky,
Comments are as follows though specific cases may well vary:
1. Condensation - the surveyor is recommending increased ventilation within the roof space to reduce the occurence of condensation within this area. They are recommending installing vents ducted all the way through the gable wall and also at the eaves via the soffits.

Not wanting to contradict others who have posted with the best of intentions but if your think about it, when you insulate a loft void by laying insulation on top of the ceilings to rooms below, the loft void becomes colder. The more insulation you add the colder the loft void will become in winter and therefore actually at higher risk of condensation and not at less risk.

To counter this effect loft ventilation needs to be adequate and if it was marginal to begin with or has been compromised by original roof vents being covered over by say plastic cladding the soffit boarding without allowing for vents then the dew point (the temperature at which condensation will occur) may well be reached.

Improving the ventilation can be done by a number of means to remove this moisture laden air from the loft void. Preferably there should be cross ventilation to create air movement so hence ventilation at the eaves by soffit vents or 'under tile / slate' vents at eaves and possibly reidge vents helps as would installing a vent ducted all the way through the gable wall. If you are going to install a vent through the cavity gable wall ensure it is ducted all the way through the wall as if you only vent the into the cavity this moisture laden will enter the cavity void and could cause localised dampness problems. Many modern roofs incorporate a breathable felt reducing the requirement for specific vents.

Many roof voids will suffer condensation to some degree and if this is relatively transient then the timeber may not decay. If however the timbers become constantly wet then decay can often occur. Please ensure there is a 50mm air gap between ceiling level insulation and the underside of any roof covering at the eaves. If my memory serves mecorrectly I think the eaves vents shodl roughly equate to a continous 10mm wide vent or equivalent if circular individual vents are used with insect mesh and weather protection.

2. Bracing of the roof trusses is to give them structural stability. When trusses first began being installed the lack of bracing from one truss to another could in some situations make the roof trusses at risk of collapsing like a set of dominos and at risk of other problems. Pre-treated softwood planks will usually suffice and a competant roofer shoudl know what is required though a roof truss manufacturer will often be happy to advise on supplementary bracing as will your Local Building Control Officer.

The cost of such work in total should not be excessive but would be expected to be at least a few hundred pounds and even more if access equipment and treatement of timbers at risk is required and accordingly competitive quotations from repuatble contractors shoudl be sought as part of your purchase negotiations. Hope this helps, kindest regards, David Aldred Indpendent damp and timber surveyor

andrewb4709

Hi,

we have had a bad problem in our house with damp/condensation, we had the loft insulated via grants and we found after that there was a problem with the exterior of the roof eg, slates, pointing, flashing, and also the inside all timber joists etc where soacking just had a firm in who use a spray foam all over the slates inside your loft which binds all the roof together basically giving you a new roof and stops there being a cold surface, which again in turn stops condensation/damp.

hope this helps.

David_Aldred

Hi Andrew,
I know of the system that you are describing but my own experience of this with the cases I see is that I would not recommend it particularly to properties where the roof pitch is getting down towards the minimum for the roof slate / tiles for an exposed property. The reason for the lack of recommendation is as follows:

1. In areas of severe exposure (which applies to many parts of the country) / low roof pitch or at least pitches for roofs that are approaching the minimum for the slate / tile in use, wind driven rain will tend to make the battens under the roof covering that are without roofing felt beneath wet and this can also apply to the rafters and to some degree wall plates / ridges and purlins. Usually so long as this wetting of the roof timbers is transient and the moisture is free to evaporate off in better weather then decay should not occur. However when the foam insulation is applied to the underside of the roof covering it is also applied to the battens and adjacent rafters (at least to the outer part of the rafter) such that this evaporation process is significantly !!!!!! and the moisture content of the roof timbers where encapsulated by the foam to their underside can be maintained at a moisture content that is above the threshold of decay with resultant premature failure of the roof timbers by wet or even worse dry rot.

2. If you ever have to undertake repair work to the roof covering the existing tiles / slates with foam insulation now bonded to the underside makes them very difficult to remove and practically impossible to re-use. Taken to its limit the result is if a roof needed to be stripped and re-fitted with new battens the roof covering would be unable to be re-used thus requiring the cost of a new roof covering and the cost of disposing of the existing roof covering. Even if you were going to put on a different type of roof covering there may have been a resale value with the old roof covering as many people require second hand slate / tiles and with foam bonded to the underside of the slates / tiles the roof covering is a complete loss.

3. It is unlikely that all areas of the roof void can be easily reached with the foam insulation and in many of the cases I have seen some areas of the roof covering fail to be insulated and these become chronic cold spots prone to concentrated condensation which again impacts upon the timbers by way of premature decay.

4. The product is often marketed as an alternative to undertaking traditional roof repairs. It should be obvious that this does not give you a new roof at all and a failing roof covering will continue to do so and ignoring a roof defect by simply applying foam to the underside of a partially failing roof covering that may have leaking valleys etc is usually asking for trouble. As indicated above when repairs do become necessary undertaking such repairs with foam bonded to the underside of the roof then becomes very difficult. The roofing contractor may quite rightly not want to get involved because disturbing the foam may invalidate any guarantee and making good of the spray bonded foam once disturbed is usually outside the scope of the average roofing contractor.

5. For people considering buying a property with this bonded foam applied to it in areas where the above problems may exist it runs the risk of discouraging that buyer because of the issues described in 1-4 and hence with a housing market that is already struggling to find buyers this could impact upon the resale value / how easily the property was to sell and is typical of something being done with the best of intentions to improve a property but which may in some cases have a negative impact by way of the issues described above.

The system is not cheap and whilst I am not saying that in all cases the above will occur, in many of the cases I have been asked to inspect this problem has been found and because of this I cannot have the confidence to recommend such a system be fitted though you obviously pays your money and you makes your choice. Kindest regards, David Aldred Independent damp and timber surveyor