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Pitched Roof Structures

 

Pitched Roof Structures

You’ve clambered up into the roof void, the attic. What’s the function of those wooden planks and what problems are associated too?

Unless it’s a flat roof, the upper most board that normally runs across the top is the ‘ridge board’. This is the apex or peak of the hipped roof.

Then running from this ridge board to the walls are the rafters. These are normally 3”x 2” in Victorian housing; in the 1930’s, the thickness was increased to 4”x 2”. Yes, imperial measurements, not metric, in those days!

The rafters have to span half the width of the house, so they are normally supported mid span by a large timber called a purlin. This stops them bowing or sagging under the weight of the tiles. We have seen purlins as thin as 4” x 3” in some properties in Gloucester Road and St George. With better quality Victorian housing, say in Fishponds, they can be up to 9”x 3”.

These are often supported mid span by a diagonal brace (called a strut) to take the loading (weight) to the central spine, the load-bearing wall in the middle of the property. Otherwise, the strut may be fastened onto binders. These are timbers spanning across between the load-bearing walls to stop the purlins bowing.

If you have read our blog on Pitched Roofs, you will know about ‘roof spread’. Sometimes even these reinforcing  arrangements were not enough, or have been removed, so additional struts were also used,  sometimes with collars. These struts run between the rafters just above the purlins, to give triangulation to the structure.This sends the weight loading down to the load bearing walls at 90⁰, preventing them from spreading and pushing the tops of the walls outwards.

Types of Roof Structure

Before the 1960s

Before the 1960’s, most roof structures were of traditional cut timbers, sometimes called “carpenters’ roofs”. As it sounds, each length of timber was measured and cut by hand, then lifted into place and secured with nails.

There were various designs of roof around during the Victorian era.  Inverted or Butterfly roofs were very common in Totterdown and Easton.  These have a central valley running down the middle to take rain water away so are prone to leakage. The structure is often problematic and cannot be inspected from the ground. These must be inspected from a pole camera or ladder. The valleys were supported by a ‘roof plate’ underneath. This was a substantial timber running under the valley from front to back.  These roof plates have often deformed under the weight of the tiles and water ingress issues have often caused decay. These roof styles stopped being used at the beginning of the 1900’s.Such roofs cannot easily be converted to habitable space as they have limited headroom.

In the 1930’s, usually in end of terrace houses or semi-detached properties, the sloping hip timbers run to the external walls.This hip is supported by a hip board or timber and the cut rafters around it are called jack rafters.

From the 1960s

Around the 1960s trussed roofs started to gain in popularity. They incorporated the rafters, ceiling joists and bracing into a large triangular structure. These were manufactured off site and craned into place.  Then they were fastened using gang nail plates to fix the joints together. They were quick to install and were cheaper in comparison to cut roofing as the skills required were less.

The early trussed roofs did have problems with gang nail plates rusting and failing; some properties in Horfield have exhibited this.  Such rusting is often made worse by condensation in the loft voids. The triangles sometimes tilted when installed and may not be straight and true. When some roof failures in the 1960/70’s were attributed to the domino effect of the trusses falling over, diagonal bracing became part of the Building Regulations requirements. The trusses then also had to be secured to the gable-end walls using metal straps to hold the structure together.  These are often missing in early examples of this type of roof structure and should be retro fitted.

OH, GOOD, IT ALREADY HAS A NEW ROOF…

roof

So you have diligently used our blog entries to guide you in viewing a property. You can see concrete tiles and the estate agent has said‘ Don’t worry,  it has a new roof!’ Why should you be concerned?!  Half of the ‘new roofs’ we inspect at in the Bristol area should have Building Regulations approvals and do not. Two aspects!  First, it’s difficult to sell a property without the correct approvals. Second,  the workmanship may not be acceptable if not approved.

As we know,pre 1950’s roofs in Bristol were usually covered with clay tiles (or slates) which were lighter than concrete.  Now it has a concrete roof  so we know from the planning portal that it is likely to need Building Control approvals.  This will ensure the roof structure is strong enough to support the concrete tiles. Also that Fire (Part B) and Energy Performance (Part L) criteria have also been met.

THE STRUCTURAL ISSUE

If it has been re-covered with concrete in the last say 5 years, then very little time will have elapsed. The building’s lifespan is a lot longer than ours!  And the faults linked with overloading the property’s roof structure can take years to develop. The existing timbers (the rafters and purlins) may be too thin to support the new heavier tiles. If they have been replaced, these may also be inadequate.

The replacement covering should have been constructed with input from a structural engineer. (S)He would have determined the loadings. He would then have checked that the load bearing walls were suitable for the increased loadings.

If the timbers have been replaced, they may have the stress gradings stamped on them. This shows the strength of the actual timbers.  C16 is weaker or C24 is stronger. The trada tables then give allowable spans depending on the centres.

Why does this matter? First the rafters will bow, causing the load(weight) of the roof to be sent at an angle into the walls. However, the load should besent vertically straight down to the foundations. This often leads to cracking around the tops of the walls, commonly known as roof spread.  This can be seriously expensive to repair.

Eventually the roof itself will deflect and the tiles become loose… look at the ridge line carefully!

 

WHY WOULD YOU SPEND SO MUCH MONEY AND NOT HAVE THE WORK APPROVED?

It is not normally the vendor’s fault! Roofing works are very expensive so it is likely that the cheaper quotes were accepted. From the roofing contractor’s  perspective,it does make life easier not to inform Building Control!  Awaiting Building Control inspections can delay payments and hold jobs up. And if the work is not inspected, the contractor would not be held liable for infringements at the time.

It is likely that this missing compliance “paper trail” is only identified when selling the house.It normally comes as quite a shock to the vendor!  Indemnities are often offered by the solicitor but thesemerely indemnify against enforcement action being taken by Planning or Building Control. They do not deal with the quality of the structure in any way.

HOW CAN YOU TELL?

There’s a very quick trade secret ! If the has been recently recovered and has less than 270mm of loft insulation present, then it would not comply and hence we know has most likely not been inspected. Otherwise, ask the vendor about the Building Control sign-off documentation. If that is not present, make sure your surveyor inspects the roof structure thoroughly, which won’t happen in a home-buyer’s report !

“Loft Rooms”

Is that converted attic described as a ‘Loft Room’ in the Agent’s  particulars? Then beware – the trick is in the wording! This is often ‘agent speak’ for conversions that do not benefit from Building Regulations approvals. Hence it is not considered habitable space and as such cannot be lived in. Nor will it be valued as habitable space by the mortgage company. ‘Loft Room’ is often a snappy short-hand for major problems with the conversion!

BUILDING REGULATIONS

The Building Regulations specify the performance factors for varying building elements. Before commencing a conversion, you should submit the proposed drawings and any structural engineer’s calculations to the Local Authority, for their approval. Council Building Control Officers or their contractors would then visit the site at intervals during the course of the works. This ensures that the works are being carried out as specified in the plans. It also ensures that the correct materials (such as concrete lintels) are being used, prior to them being hidden by plaster or render, for example.

Some surveying companies offer this service commercially, so you can use their approved inspectors rather than the Local Authority for approvals. This may save you money and these organisations can offer a more flexible verification process.

Then at the end of the works and on the final inspection, a Completion Certificate is issued to the building owner or their agent.

WHY IS THE CERTIFICATION IMPORTANT?

The information and certification produced in this process is vital for later surveyors!  We do not routinely break into the fabric of the building in the course of our inspection.  If we did, the vendors would no doubt be very angry as holes in walls are not ideal when selling a property!  The Completion Certificate states that the conversion has been inspected and meets the compliance standards in force at the time of the construction.  Are you hoping to sell a property with an attic conversion but no Completion Certificate? If so, you may be disappointed at the price you finally achieve.

WHAT ACHIEVING COMPLIANCE IS LIKELY TO INVOLVE

Just taking one section of the Building Regulations as an example, Part L : the Conservation of Fuel and Power Regulations. These are designed to reduce the amount of fuel needed to heat a dwelling. Part L describes the need to hit certain “U-values”. These are performance factors of materials used in the construction of the external envelope (walls and roof). Nowadays you would be expected to have significant thicknesses of insulation in the slope of the roof for it to be signed off. Compliant materials would include Polyisocyanurate board, also referred to as PIR or ISO, a yellow type foam insulation with silver foil on both sides. The alternative would be expensive multifoil or equivalent.  Such insulation is rarely found in non-compliant older structures.

 

HOW TO MAKE THE LOFT ROOM COMPLIANT WITH PART L OF THE BUILDING REGULATIONS?

You would have to strip out all the existing internal plasterboard on the walls and ceiling in order to fit such insulation.The Regulations also normally require that insulation is left beneath the floor and again this may not be done. To check whether it is present, the floor may need to be stripped out, even partially. And the floor may need removing completely to insert such insulation to create a compliant space.

SOME OTHER CONSIDERATIONS

Other sections of the Building Regulations include Part B, bought into sharp focus in the wake of the Grenfell tower disaster. Part B Regulations cover fire safety and the need for fire resisting corridors for safe access, fire doors, smoke alarms and heat detectors. For example, does the attic conversion have fire doors? Or a robust staircase escape route?

And then there are the comprehensive Electrical Regulations to take into consideration!

SO IS THAT ‘LOFT ROOM’ AN ASSET?

In summary, if the conversion has to be stripped out to ensure just one factor is met, this will be costly. To remove the old non-compliant structure,you will have incur labour costs to dispose of the old materials, before you upgrade the conversion correctly. Compare this with purchasing a property that has no ‘loft room’at all and then converting one properly…

 

Lofts and Attics

Lofts and Attics

Loft spaces

You are unlikely to get access to loft spaces when doing a general viewing. It’s easy to put your foot through the ceiling below when you slip on a joist! And this will be on the vendor’s household insurance or agent’s insurance so you would not be popular. So don’t be surprised if the agent will not let you check the loft void.  Just smile, knowing we will check it thoroughly for you after you have made your offer.

However, you may be allowed to poke your head and shoulders through the access hatch, as for a homebuyer’s report. Or you may be buying a property privately.

Precautions

Checking lofts is not for the faint hearted as spiders, wasps, mice, flies and rats also make these locations their homes. If you don’t like creepy-crawlies, don’t go exploring in a strange loft!

Some of the older types of loft insulation have been known to contain asbestos. So do be careful and wear a PP3 level mask before opening any loft hatch of an older property.  And carry a torch with a long beam, as very few loft areas have lights.

There are three main aspects to consider in loft spaces:

Sarking Felt

Roofing (sarking) felt is designed to keep the roof waterproof, lying beneath the tiles. It should stick out into the gutters.

One of the best easy tests is to simply turn off any torches or lights and look to see if daylight is visible through the roof or eaves. This suggests holes in tiles and felt or detailing (finishing) problems.

If the black bitumen type felt is present, this is a much older felt.If there are large rips or tears present, it may need replacing.This is a very expensive job -say £6k+.Differing colours of felt indicate where patch repairs have been made internally. These are rarely successful and again replacement in probably necessary.

Is the felt white, blue or green coloured, with tiny dimples? This suggests that the roof has been recovered in the last 20 years with a stronger breathable type of felt and should have a long service life left. However, look for rips and tears, due to poor installation. And condensation can still cause mould growth.

Timbers

The main things to look for are split or bowing timbers in a roof structure. Cracked timbers are often very noticeable as the sharp edges and shear nature of cracks tend to draw the eye. Rafters, struts and braces can often be strengthened internally without the need for expensive scaffolds.

Where major components such as purlins have bowed, this is seldom an “easy” fix. It may have been caused by heavier replacement roof tiles, for example.  Often a new larger purlin will be required, at considerable expense.

Bowing timbers change the way that load is carried through the building. Bowed purlins and rafters do not transmit straight down at 90° and instead push outwards.This puts additional stress on the masonry. When rafters dish in this manner, it can cause” roof spread”, damaging the supporting walls below.

Keep an eye out for patches where the timbers have clearly been stained by water in the past (or at  present!) This is most likely around chimneys, where the flashing above has been damaged.  Rot may have already set in.

Insulation

With the ever-increasing cost of heating, loft insulation has been retrofitted in many homes.

Beware! Older types of insulation were vermiculite, gold shiny coloured lightweight pellets and blown cellulose which looks like tiny fragments of newspaper – which is often what they were. These types have been known to contain asbestos. If these are visible, don’t go any further into the loft – be thankful you are wearing a mask!

Sometimes the loft floors have been boarded so it is difficult to add insulation.Modern Building Regulations require 270mm of mineral fibre. This is rarely achieved as the rolls normally come in 100mm thickness so 200mm is more usual.

Sometimes the insulation has been poorly installed or has been pushed right into the eaves. Then the loft space can’t breathe or ventilate itself. Condensation then builds up inside the roof void, damaging the timbers in the unseen areas in the eaves.

Gutters

Examining gutters and downpipes

Background

The UK is a wet place as we all know!  The Bristol area averages around 800-900 mm of rainfall a year, which is slightly above the UK average. Even more rain fell in recent years such as 2012 with weather conditions changing. Interestingly, in the past, South Bristol has been wetter than North Bristol.

So this rainwater must be diverted from your roof into your gutters, on its way to the drains. Gutters don’t just remove rainwater, they are an integral part of the house design and character!

They should prevent water from penetrating the tops of the walls and leaking gutters can often cause dampness problems. Furthermore, this is sometimes wrongly diagnosed as rising damp and a large inappropriate repair bill follows – although just replacing the gutters would have solved the problem.

Materials  and Styles

Gutters have traditionally been made from many different materials. Historically, timber has often been used in the north of England, usually lined with lead. More common to Victorian era housing is cast iron and this is prone to rusting. In older properties, especially around South Bristol and Clifton, the gutters may be hidden behind parapet walls at the front of the property. Some Bristol properties have ‘butterfly’ roofs, where the gutters run in a valley hidden behind this parapet. Hence in such cases, inspection from ground level is impossible.

More recent  gutters can be made from asbestos type cement, which therefore will be expensive to remove. Fortunately,   you can carry out a simple check for asbestos gutters and pipework with a magnet;  see our  video https://youtu.be/tfihb5NdZRk . Recently, some gutters, especially long runs, have been made from extruded metal, usually aluminium, but the most popular material is UPVC – ‘plastic’ guttering.

What to look for?

Gutters

Now, you are looking for evidence of leakages and blockages.

Can you see any organic growth sprouting out of the gutters? That’s a sure sign that maintenance has been poor. Are there any overhanging trees whose leaves may have blocked the gutters in autumn?

Next, stand back from the building to check that the gutters are set to the correct falls. They should run in a straight horizontal line towards the downpipe with no dip or deviation.

Rainwater Goods Fastenings

Gutters should normally have supporting clips  spaced at around 750 mm apart. Since the average man’s footstep is around 780 mm, you can pace the length of the gutter with an “average” man and there should be 1 clip per footstep. However, if sufficient clips are not present, the gutters can twist or bow or sag. When this happens, the correct fall is lost and they will start to leak as the weight of water causes pressure which damages the joints.

The joints between the lengths of gutter are usually located at the clips. Hence this is an easy place to look for heavily stained or soiled clips, suggesting leaks in these areas. And if a gutter has been leaking for a long time, stalactites may have formed on the underside of the gutter where water has been dripping. Another great giveaway is staining to the wall; this normally takes the form of darker streaks or patches or green algae or moss growth on the wall. Take note, because this will certainly indicate problems not only with the rainwater goods but potentially inside the property as well.

However,unless you can find a high level vantage point, you won’t be able to see inside the gutters; we use mast cameras as standard on our building surveys to check for blockages and detritus in the gutters.

Downpipes

Now look at the junctions connecting  the gutter to the downpipe; these often incorporates an arrangement of curved sections. These joints are not normally supported by clips and are vulnerable to movement hence they are always susceptible to leakage. Again, this is a very common fault so look for moss growth or staining around the joints.

The downpipes should have clips securing them every 1.8 m. Again the average man is around 175 cm in height so this is a good datum. Downpipes often become blocked with moss and other detritus. So give them a knock to see if they sound hollow; if a dull sound is heard, then they may be full of moss and need to be cleared out.

The modern UPVC extruded parts for guttering and downpipes are very cheap to buy and the largest cost with installation is normally the labour element. As a result extensive repairs to gutters are normally a bad idea! Simply replacing them and obtaining a longer life is usually a better use of your money.

Where does that water go?

Lastly, are there any water butts at the foot of the downpipes? If so, are they overflowing into the foundations of the property? Do the downpipes lead into drains or do they splash their contents over the ground beneath, encouraging dampness, especially around bay windows ? We deal with dampness in another section, but the condition and design of the rainwater goods can give you some valuable pointers!

 

Pitched Roofs

roof

Pitched Roofs

Roof repairs can be very expensive, not just the materials and manpower, but will possibly require scaffolding as well. So take binoculars or a camera with a powerful zoom to enable you to visually inspect the roof covering.  You can do this at any time, without the agent having to be present. As always, look at the neighbouring roofs see if they have recently been re-covered, a good indicator of when yours will need doing.

What is the roof covering ?

Next, focus on an individual tile and try to determine what it made of, clay (older) or concrete (more recent). In some areas, older properties have real slates. Concrete tiles indicate a post-war roofing replacement. Is there anything special or unusual about the type of roof tile? Some tiles such as Triple Deltas and Bridgewater tiles are not as readily available as more common types such as Pantile or Double Roman.Hence they are more expensive to repair or replace.

Can you see any defects?

Are there any slipped or missing tiles? These indicate a lack of routine maintenance but also water ingress is very probable.  Water can cause damage in a timber loft space which can be very expensive to repair! If there is some lighter colouring of the surrounding tiles, this may indicate a more recent break or slip.

Is the roof a “patch work quilt” of differing colours of tiles? Probably someone has made many repairs and it may be time to replace the roof covering completely. Also, look out for small grey tags known in Bristol as “tingles”; these metal (usually lead) clips are used to secure individual tiles and they indicate localised repairs have been carried out. If you see any grey coloured tape, this is normally called ‘flash band’ and is used as a temporary repair. However, it is simply a sticky tape and cannot be considered permanent – the defect should be properly repaired, not just taped over!

Can you see any ‘lifted’ tiles, ones that are not lying flat? If so, there could be a problem with the roof structure beneath. Where the property is in an exposed elevation, the tiles may be vulnerable to lifting by wind and regular repairs will probably be required.

If there are a great many slipped tiles, possibly the roof is suffering from ‘nail fatigue’; the nails have started to rust away and can no longer hold the slates in place.Although such failures may occur in a localised area initially, it is highly likely to occur more widely in the near future.

Man-made regular roof ‘slates’ can be asbestos containing. They are fixed centrally with a single nail and may start to ‘ cup’ or dish. When this happens, the life span of the roof covering  becomes  very short.

Get an overview of the roof structurally

Finally, try to check the structure. Look at the condition of any mortar such as along the ridge or the hips. If the mortar is missing, this indicates lack of routine maintenance.These areas will require repairs at the very least and possibly more extensive remedial action.

Is there any ‘dishing’ to the roof covering?Do the tiles lie in a straight line? If not, this suggests an inadequacy in the roof structure beneath, possibly very costly to remedy.

 

 

Chimney

chimney 2

Chimneys

 

Chimneys and their pots come in many shapes and sizes. Some are easy to view, others less so. Chimneys can be costly to repair because access is awkward and expensive as scaffolding is usually required.The main problem with chimneys is their propensity to allow dampness into the property.

Simple Checks

  • Have a look at the top of the stack – can you see any chimney pots present? if not they may have been removed and not capped off – in Bristol there are lots of open chambers where the pots have been removed and rainwater can run straight down inside the stack.
  • Now run your eye down the stack, looking for any obvious failures in the pointing, (missing pieces of the mortar that bonds the brickwork together). The pointing should be in good condition to prevent penetrating dampness and to shed rainwater down the surface of the bricks (or stone) and away onto the roof. Older stacks are likely to be pointed with lime mortar rather than sand & cement. In Bristol, Buddleia are often found growing from the lime pointing of the stack or from parapet walls and the roots can cause damage to the brickwork
  • Next, stand directly in line with the stack in front of the chimney and see if it leans. Whilst some misalignment may be acceptable due to prevailing winds, even a slight lean may signal a defect with the roof below or the condition of the brickwork.

You are unlikely to be able to see clearly the very top of the stack, the cement holding the pots in place (flaunching), the lead flashing surrounding the stack and the actual condition of the chimney pots or caps, but we can help. We always use our mast cameras as standard when undertaking our full building survey to help us inspect in detail the parts you cannot see.(https://www.youtube.com/watch?v=balBNOI64k0)