roof surveys
An example of a homeowner roof survey
Throughout this report, I will be referencing the relevant BS numbers for lead sheet and slating & tiling for pitched roofs (BS 6915 & BS5534 respectively). As you can guess, these two codes of practices work in conjunction with each other to provide the standard for installation of all supported lead flashings and pitched coverings. Throughout the survey I accessed as many hidden parts as possible that were safe to do so. There are still hidden parts which I could not access, as such some parts of the roof weren’t surveyed.
The roof has been constructed with breathable felt (Quality, brand and product unknown), treated battens, natural slate and dry verge and ridge systems. The batten fixings are unknown. Due to the appearance, it is assumed the slate are Brazilian. These slates are classified as a “Mudstone” and are typically unpredictable when it comes to the harsh British weather. They have not undergone the full metamorphic change to become a true slate. As such the strength and brittleness of the slate can be severely impacted. Brazilian slates don’t react well to the expansion and contraction elements which are common in this country, over the different seasons. This is especially important to point out as they have used steel galvanized nails, which will severely limit the amount of movement. This can lead to slates breaking. However the material would have to be confirmed with the supplier. The slates have been fixed with a 30mm steel galvanized clout nail (Sampled from one area, Evidenced in photographs). The valleys have been formed with code 4 lead. The main features of the roof are as follows.
• Large apex to front elevation
• Small cladded dormer to front elevation
• Large area verge to verge with numerous Velux windows (Rear elevation, Upper roof)
• 4x Lead valleys (Upper roof, front elevation)
• Verge to abutment (Lower roof, above garage)
• Lean to roof (Front garage)
For this report, I have provided an aerial view of the property and split the different sections into coloured boxes for
ease of referencing. These are as follows:
• Red box – Front elevation, Upper roof
• Blue box – Front of garage
• Green box – Rear elevation, Upper roof
• Yellow box – Lower-level roof above garage
Breathable Membrane
Some breathable felt materials as part of their installation specification specify that other ventilation means must be introduced. This can be done by cross battening, installation of eave vents, slate vents, soffit vents and leaving the felt open at the ridge tree. This is because different qualities of membrane have different vapour permeability’s (Meaning the better qualities allow more vapour through). As this roof doesn’t contain any other ventilation products (Apart from dry ridge system), It would require further investigation to see if this could be a condensation risk. The specification for material would have to be acquired from the architect.
Nails
BS 5534 states that all roofing products when fixed should penetrate the batten by at least 15mm. Nails should be 20-25mm longer than the two thickness of slates combined. The thickness of slate provided was measured at 8mm (16mm for two), Therefore a fixing of at least 40mm should have been used to achieve an adequate fixing. This is especially concerning considering the elevated pitch, where gravity and high winds could eventually cause slates to come loose and dislodge from the roof prematurely. This is an obvious health and safety concern considering this structure is inhabited.
On average, a well-constructed natural slate roof should last between 80-100 years. To achieve this a copper nail should be used. Using copper nails prevents rusting and will easily last the lifetime of the roof. Using a steel galvanized nail is a cheaper alternative, however we can expect these to fail and rust considerably sooner, bringing the life cycle of this roof to an end prematurely. A steel galvanized nail is also too tough for natural slates. They make future maintenance considerably harder and expensive. In the interest of longevity and performance, a copper nail should always be used.
Yellow box – Pitched roof above garage
Inspection of the rear elevation above the garage revealed several problems with the lead flashings to the abutment wall. The front lead apron underneath the soffit has no upstand and lays flat, BS 6915 states that a lead apron should have a minimum of 100mm upstand, this is necessary to provide lead to be bossed or welded around the corner, creating a watertight corner. As there is no upstand, there will be minimum coverage from the soaker above, there is a risk that water could track up between the two flat surfaces by capillary reaction. On the rear elevation, it appears that the main roof was finished first, because of this access was limited to install cover flashings above the soakers (Poor planning). Every soaker on the rear elevation is exposed, this is a serious problem where driving rain that hits the wall, will allow water to run down and into the roof void. It also appears that a small soaker has been inserted 3 courses from the top. This has likely been put in as there wasn’t sufficient lap (Minimum 75mm on soakers). As access was restricted, it is unclear if there is a lead saddle (Which is molded across both elevations) under the ridge. From a distance it appears that this has been bent and cut around the ridge, further inspection would be needed to confirm.
Numerous cracked/broken slates could be observed across both elevations of this area.
Blue box – Lean to pitched roof in front of garage.
Inspection of this section of the roof revealed the roofer has gauged the roof out wrong. He has left a void at the top of the frame allowing for the lead flashings to sink into. There is a section of lead apron that appears to be flat after it’s begun to sink behind the batten. This can cause water to run sideways through the flashing, causing water ingress.
Inspection of the lead aprons revealed that three of them had insufficient side lap. BS 6915 states that a lead apron’s side lap should match the minimum lap onto the slates (150mm in this case). As you can see from the photos, these are below that amount. Inspection revealed that a bead of silicone had been added at some point, I assume that this had leaked during construction and the roofer did a repair on this section as he has not done this to
any other flashing.
Inspection of the internal corner where the apron meets the side abutment revealed incorrect and defective flashing. As evidenced by the photographs, persistent rain will simply capillary react across and leak into the cut soaker. Please find below an illustration of the correct flashing with an example. The example has been welded together to create a watertight finish.
In addition to these faults, where the lead apron meets the overhang to the external wall, the apron has been cut flush with brickwork. The lead flashing should have been bossed/welded around the corner to protect exposure. As a result, the corner of brickwork is exposed to the elements and there is a risk of water penetration into the garage.
One defective eave and slipped slate was noted in this area.
Green box – Upper rear elevation
The rear elevation of the upper roof is of simple verge to verge design with numerous Velux windows installed.
There are numerous cracked/broken slate which can be observed across the area of roof.
Towards the right-hand side where the pitch changes, the continuous dry verge has been cut. I presume this has been done as the pitch change would have prevented this bending. However, they have not used a coupling to join these two now separated pieces together. Water that runs down the channels will now run into the cut, saturating the felt. There is a risk that water could then travel through the nail holes in the felt, deteriorating the
timber work. You can also observe from the photos that the bottom piece of the continuous verge has been cut short, leaving the corner of the facia exposed.
Red box – Front elevation upper roof
Inspection of the front elevation revealed numerous serious problems to the leadwork and valley details.
Inspection of the front right-hand side corner of the dormer revealed installation problems with the lead apron and soakers. The lead apron should be bossed/welded so that it lies flush with the timberwork of the dormer.
The bottom soaker doesn’t come down far enough to be bossed around the corner, providing adequate coverage. This has left the corner exposed. Water coming down from valley above can penetrate this corner allowing water ingress.
You can also observe from the photos that the cladding has very little coverage onto the soakers. Water has the potential to drip and splash up the cladding and behind the soakers. The minimum coverage that the cladding should overlap the soaker is 75mm, which you can clearly see is below that figure. In addition to this, the minimum width a soaker should be under the slate is 100mm. Although they may be 100mm, they haven’t been dressed correctly into the dormer, because of this it has made installation of the slate more difficult. As you can see the slates do not sit flush into the corner of the soaker, reducing the recommended side lap to below 100mm.
Directly above these soakers where the valley joins into the roof, you can observe that the lead soakers have almost no upstand and are level with the slate (One is completely missing, leaving felt completely exposed). In addition to this, the gutter and valley drain into this section and behind the soakers. This is a critical detail which has been very badly installed. The valley is likely to be currently leaking, causing internal damage and should be rectified
at the earliest opportunity.
I also observed that the length of the valley was too short (both valleys to the dormer are too short). The valley should come much further down and be bossed up and against the facia and into the eave above.
This allows plenty of coverage to the soaker and slate below. Typically, the bottom and top pieces of valley should beof code 5, this is because when you begin to boss the lead, you take thickness out of the lead sheet so that it becomes less than code 5. As these valleys are entirely made of code 4 lead, these pieces of lead will now be below to minimum code for a valley. BS 6915 states the minimum code a valley should be is 4. This is also why one of the valleys has split entirely at the bottom.
The ridge adjacent to the top of this valley is too short, leaving the membrane exposed. It is also completely loose. As per BS 5534, mechanically fixed ridges should have a minimum of two fixings at every junction.
Inspection to the base of left-hand side valley to front apex revealed incorrectly installed leak soakers, with several splits noted to the bottom piece of valley. It is likely the roofer found this detail difficult to boss around the facia due to how steep the roof is. This has probably influenced his decision to lay the rest of the valleys short. BS 6915 states that the minimum code a valley should be for this area is 4. As they have attempted to dress this round, they have
decreased the thickness of the sheet which is no longer acceptable.
At the top valley junction of the large apex, the two top valley pieces have been cut short. This has left the membrane exposed, which has been damaged revealing the valley boards exposed. This is an active leak and should be rectified immediately before internal damage is caused.
They have also used a lead saddle to cover an area where they were a ridge short. This lead saddle is completely loose and offers no water protection where it joins the ridge next to it. The end ridge only has one mechanic fixing, BS 5534 states that must have a minimum of two fixings.
Summary
There is evidence of very poor workmanship throughout this project. There are a lot of lead details which are incorrect and likely to leak, as well as a few serious problems which are actively leaking. As I understand, choices of materials were scarce as this project was built during the Covid-19 global pandemic, which probably led to the decision to use Brazilian slates. The choice of materials would not have helped in the installation of this roof.
As the installer has used 30mm galvanized clout nails on such a steep pitch, there is no suitable penetration into the batten. This has not been installed to British standard and could cause slates to dislodge under their own weight and especially in high winds. I would argue that this roof needs to be completely re-done just off this basis.
However, to correct the defective areas of the roof, you will have to strip out large sections of slate in order to correctly access them, such as the valleys, cladding, abutments, facia, barge boards etc. At this point you would reveal more hidden sections and be able to observe if the roof has been felted/battened correctly as well as forming the valleys correctly. This is likely to cause major damage to the surrounding slate as they’re so brittle and
most will not be re-usable.
In my professional opinion, this roof needs to be taken off and installed properly, with the right fixings and lead details, working to the current British Standards. The problem however is that we estimate 20% of the slates could be re-used, of which these are likely to be damaged during re-installation. The rest will be unusable and will unfortunately have to be disposed of. Therefore, it is a very real possibility that you could have to replace the full roof worth of slate.
To guarantee any kind of work, the roof will have to be stripped back to nothing, re-felted and battened and installed again correctly. Scaffold will also need to be erected for the safe access and egress onto the roof.
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