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How To Replace Concrete Gutters: The Right Way

I think it’s time that all the myths and rubbish talked about concrete or Finlock gutter systems, was finally swept away. I have been involved with concrete gutters for over 40 years, both as a surveyor for housing associations and for a large county council. I have seen every stunt and cowboy trick that could be pulled. I have written specifications for concrete gutter replacement which entailed working with manufacturers, suppliers and contractors to deliver consistently high quality effective solutions to overcome the problems caused by concrete gutters. I now run a design and build company which occasionally is asked to remove concrete gutters. We are considering actively promoting concrete gutter removals, but that’s largely because I see it being abused by sales organisations with little or no technical expertise providing poor value for money, paying sub contract labour peanuts whilst supporting sales leaches who make over 50% commission on the overall cost of jobs. I am appalled by the blatant self-advertising, puerile spam evident to all but the most gullible (unfortunately they are the targets of the most unscrupulous of the majority of rogues that seem to infest concrete gutter replacement) that I have seen on blogs relating to concrete gutters. Well read on, and maybe some of the cowboys out there will gain an insight into how to do the job properly. I am sure that you will see that there is no mysticism or rocket science involved – its common sense really.

Generally the problems with concrete gutters are:

  • Poor aesthetics
  • Leaking at joints
  • Displacement above windows (often caused by poorly fitted PVCu replacements where the installers failed to recognise that the original windows where partially supporting the cantilevered concrete blocks above the window heads. There is a lintel tray above the inner leaf of the cavity wall which was filled with concrete or mortar with a few steel rebars thrown in, often quite indifferently)
  • Thermal bridging.

The biggest problem with concrete gutters is generally cold bridging. This occurs because the concrete Finlock Blocks bridge from the outside to the inside of the cavity. The wall below is thermally broken from outside to inside by a cavity, generally retrospectively filled with a modern insulating material. Thermal bridging cannot be cured by relining thus removal is the only option to ensure that the endemic problems are eradicated.


The Concrete Gutters should be carefully measured. Any obstructions such as cabling, security lights etc. should be noted. The roof should be examined internally and externally to assess the condition of the roof and sarking felt. (It’s pointless replacing the gutters if you need a re-roof, better to do both jobs at the same time to reduce overall costs such as scaffolding). Any displacement above the windows should be noted and in extreme cases where the deformation to the window heads is severe, arrangements made for additional support in the form of lintels. These can generally be formed with 152 x 102 x 9.5mm steel angle to BS 4 1993 for the majority of spans that will be encountered. They should have a minimum bearing of 150mm on either side of the window reveal. Usually the removal of the cantilevered concrete gutter will reduce the dead load on the window heads negating the need to provide lintels and the displacement will be hidden once the new fascia profiles are in place. Also, if a strong 38mm x 150mm backboard is used, it will add strength and stability to the remaining concrete gutters.

A preliminary assessment of any dangers such as asbestos should be made. Asbestos cement rainwater pipes and packers to the concrete gutters are quite common. Don’t panic if someone tells you that you do have asbestos rainwater pipes: The HSE regard it generally as low risk, (read their asbestos essentials leaflet EM9). You don’t have to be a certified asbestos removal company to remove small quantities of asbestos cement, householders and general contractors can remove it (contractors must be insured). As a householder you can usually remove it yourself and arrange to take it to the local authority for disposal at no cost (check with your local council). Your local authority will normally provide you with the correct double bags and labelling. For more information see HSE asbestos essentials sheet a14. Either way, arrangements for the safe disposal of the asbestos must be made, and the client should keep a record of the waste consignment note. Contractors must have the asbestos containing material disposed of and a waste consignment note should be given to the householder. Generally the cost of disposal on small amounts is £130 -£210. Commercial operators need to be registered carriers and will need to fill in a Consignment Note before disposing of asbestos cement.

A photographic survey of areas affected by subsequent works should be under-taken, which may form the basis of evidence of condition should a dispute arise. It should be noted that on semi-detached properties and terraced houses, the concrete gutter is in effect a party structure and as such places a legal obligation upon the property owner to adhere to the Party Wall Act 1996, thus a notice should be served on the adjacent property owner or owners, advising them of the work (you can download a standard letter and serve the notice yourself). If you have a good relationship with your neighbour and the work is performed well, it is likely that this will be the end of your Party Walls involvement.

Roof area should be calculated and the size of gutter system which will safely discharge rainwater to the drainage system determined. Generally an Ogee profile gutter will have sufficient capacity to safely discharge water from the roof; sometimes it is advisable to fit a deep flow gutter profile and 100mm down pipes. If in doubt, a deep flow profiled gutter should be used.

A risk assessment should be made to identify any potential hazards or problems so they can be negated. If asbestos is visibly present it will be identified in order to facilitate its safe removal and disposal.

Another consideration which should be taken into account is whether bats are present, or are likely to be present at some time during the year. If so any works which would adversely affect their habitat must be avoided. Generally if you have an indication that bats will be affected by the work – don’t fit any form of control which may prevent their entry to (see below in method 2) the property. Don’t be tempted to avoid your legal obligations, bats are fiercely protected by legislation. Fines are hefty and if your house is an important roost, you can guarantee that local bat lovers will know all about it.

Some companies will be able to leave you with a fixed price quotation; others may need to return to the office to prepare a written quotation. I would consider the latter as being the most worthy of your trust, simply because someone has sat down and thought it through and is less likely to miss something out which will adversely impact on the quality or delivery of the project. Also, there will be no pressure to sign on the day, indicating that you are dealing with a contracting organisation and not a direct sales vehicle with a salesman desperate to make a large commission out of you.

Things to look out for are:

Full break down of the costs, including skip hire, scaffold hire/erection, exactly what they are going to do, i.e. extend rafter ends, contract terms and conditons, whether they will fit bird combs, over fascia vents, eaves protection, strip tiles and replace felt etc., name of product manufacturer, type and colour of profiles, details of warranties and guarantees. Ask for copies of all receipts for materials, scaffold and skip hire – that ensures that they can’t fleece you by inflating prices and that they are supplying the products they say they are. It is perfectly normal for the contractor to put 20% on materials and services which he pays for up front. Make sure that they have the necessary insurances covering public and employee liabilities. If it’s a builder, don’t be put off by him trading from his home address – you’re not paying for a sales team or his office premise – so as long as he can provide references, it is probably to your advantage. Sales orientated companies can set up and move office within days, so someone trading from home is far more likely to be reached if things go wrong, especially if they are local. Don’t be pressured into signing anything on the day, and remember that they are obliged by law to give you a 7 day cooling off period, even if you do sign. Any ethical company won’t sign contracts with vulnerable people without them being accompanied by a relative or friend who can help them make an informed decision.

Risk Assessment and Desk Top Preparation

Once the decision to go ahead has been made, a written risk assessment and method statement should be produced, detailing how any specific site hazards are to be dealt with. It is acceptable to have a written contract detailing start and completion dates, scope of work, warranties and schedule of payments. A calculation based on roof area, pitch, size and number of rain water outlets should be performed to determine that a suitable size of gutter section, rainwater pipe has been chosen. I would strongly advise that you do not sign any contracts which entail up-front payments. I would recommend that a fair schedule would entail, 10% deposit (if any) 25% on delivery of materials, 65% within 1 week of satisfactory completion. Most bona fide companies will take BACS and card payments, which can leave a valid paper trail. It is important that any issues such as sanitary facilities while the contractors are on site, are arranged, i.e., can the contractors use the house facilities or will they have to make alternative arrangements? : Nearest Accident and Emergency etc, emergency numbers for all parties.

The Party Wall Notice, informing that work to a party structure is to commence, together with a drafted acceptance letter, Party Wall Act guidance Note, should be served on any adjacent property owner. The time limit for a notice of this nature is 2 months, however a response is required within 14 days of serving the notice. If no reply is received within 14 days a dispute is deemed to have arisen. If the adjacent property owner consents, in his reply to the notice, work may commence at any agreed time. If he dissents, you have a legal right to perform the works, but will need the services of a Party Wall Surveyor. Unless a dispute is in effect, The Party Wall Act itself will not come into play. In practice, it is better to serve the notice during a friendly chat, thus ensuring that the formalities are observed just in case things do go wrong whilst retaining the good will of your neighbour.

Arrangements for any asbestos removal required must be made. A timetable showing dates of key activity should be issued to the client, showing date for scaffold erection, skip on site, contractors start date, contract completion date, date for removal of scaffold and skip.

Site Preparation

A full pole scaffold along with toe boards should be erected by a certified scaffolder. This is important for two reasons;

1)     The scaffold will protect you and your property from falling dust and debris.

2)     To have men cutting heavy concrete blocks from lightweight towers or easi dec ladders and boards is not acceptable in terms of health and safety. If the company you commission is professional and good at the task they won’t cut corners and they won’t want to put their operatives at risk. A full pole scaffold to 2 sides of a domestic semi-detached house will cost between £950 – £1700 depending on which part of the country you live. Don’t forget that whilst on your property you have a moral and legal obligation to see that the work is conducted safely, for your properties inhabitants, the operatives and any visitors. If you see anything that you feel is unsafe or a risk to health and safety. Tell the contractors, and as a final resort, ask them to stop work until you have cleared your concerns with someone in authority.

A skip should be conveniently positioned on site ready for disposal of the concrete and debris to be disposed of.

Any sensitive areas should be covered and arrangements made for their protection. (For instance fish ponds, flower beds etc.).

Any asbestos (usually the rainwater pipes) should be removed, correctly sealed and labelled and picked up by a licensed removal company for safe disposal. You should ask for a copy of the disposal note or have a copy sent to you with your paperwork for the project.


There are three effective methods of removal:

1)     Complete removal of the Finlock Blocks.

The first 3 courses of tiles are taken off. The gutter lining if any is removed.

The roof trusses or rafter feet are supported on props from the inside of the property, floor to floor and the Finlock Blocks are removed. Alternatively, if the rafter feet are to be extended it may be possible to provide temporary support externally using the extended rafter feet. The internal wall is built up with a 50mm course of cut block, and a 100mm x 100mm grade C16 High Vac Pressure treated use class 2, service life 15 – 30 years, wall plate is fixed to the top course with proprietary straps at centres not exceeding 2m.

The external wall is built up to the roof line (usually two courses). The rafters may be extended using several methods, the simplest being to plant a piece, sized according to the existing rafter, onto the end and then use another piece as a side plate, as a rule of thumb ensuring that the lap is twice the distance of the extension and a minimum of 600mm, using plate connectors to join the pieces of timber,. Grade C16 and pressure treated as before use class 2. It is good practice to close the cavity using a thermal, flexible, fire resistant material such as mineral wool.

Fascias and soffits of your choice are fitted, together with a suitable gutter profile (as per method 2). Ventilation to the roof void to current building regulation standards should be installed as part of the process, (Equivalent to 10mm continuous ventilation in most situations, except where the ceiling is to be underdrawn to the roof soffit, when 25mm of continuous ventilation is required) together with eaves protection and vermin control as detailed in method 2.

This method is costly, will cause major disruption to internal ceilings, plastering and decorations. The only time this would be a viable, cost effective option would be in conjunction with a roof replacement or major internal refurbishment. It is the best method as it introduces a continuous cavity and therefore a complete thermal break where the Finlock gutters have been removed.

2)     Cut off method 1 

The first row of tiles is taken off or pushed back. Any gutter lining is removed (if lead lined it is classed as “special waste” and should not be mixed with other debris), being careful to leave enough of a tail to make good later. The existing concrete gutters are carefully cut off in line with the external brickwork of the wall using a rotary saw with a clutch, which takes a 14” blade. A 14” blade is the smallest size which will cut completely through the 150mm thick concrete gutter system. The Square profile blocks are 200mm in depth and will need either a ring saw or one of the later diamond chain saws to achieve the required depth. The blocks should not be smashed off as this can damage the remaining block compromising its integrity and negating its use as a fixing medium. The blocks should be removed from the scaffold as work commences, preferably with a chute discharging into the skip. The cut concrete should provide a straight and plumb surface to fix to. Again the rafter feet can be extended as per the full removal method. It should be noted that although it is possible to extend the rafters, it is not aesthetically pleasing if a neighbouring property is to retain its concrete gutters. Also, it does increase the cost as an extra row of tiles will need to be installed and the gable ends will need some alteration to accommodate the additional distance created at the eaves. It is true that extending the rafter feet does improve the thermal  properties of the installation, but only by a minor amount as the air void is large, allowing cooling convection currents to negate any appreciable improvement.

If an F shaped starter trim is to be used to receive the soffit, this should be fitted before the timber backboard and screwed with 30mm x 4mm stainless steel screws to the face of the concrete at 600mm centres.

A 38mm x 150mm structural grade C16 ( pretreated by high pressure vaccuum to BS 8417) timber back board is frame fastened to the remaining face of the concrete concrete gutter to provide structural strength to the rest of the installation. It should be fixed with stainless steel fixings at centres determined by the frame fastening manufacturer (Fischer fastenings N6 x 80/50 S (100) is a 4mm diameter knock in frame fastener made form austenitic stainless steel, each fixing will support a 20kg load with a safety factor of 4, 2 fasteners per metre, double fixed at 100mm vertical centres will adequately sustain all imposed loads). Some companies use a 25mm back board which will not meet the requirements of any major UK roofline supplier or the Plastic Federation Fixing Recomendations for PVCUe profiles, as the fascias need 30mm of the fixing to penetrate into the substrate.

Next, the insulation layer should be fixed. This will prevent cold bridging and the formation of condensation and subsequent mould and damp to the inside of your property. A 25mm layer of PIR insulation board is screwed to the backing board. Together with the timber back board, 16mm of PVC-UE profile, the completed installation will have an overall u value approximating to that of the cavity wall below (even with retrospective cavity fill). A typical 1960’s cavity wall will achieve a u value of 1.8 – 1.5, with retrospective fill 0.48 – 0.9, today a new cavity wall is typically 0.3. The aligned thermal qualities of wall and remaining concrete gutter block, should prevent cold bridging and damp problems, by achieving a calculated u value of 0.47. Clearly this is a considerable improvement on the concrete block alone which has an average u value of 3.8.

The u value of a plastic fascia placed onto a 25mm backboard over the remaining concrete cut off gutter (which is what most concrete gutter replacement gutters provide) achieves a u value of just 1.52, which still doesn’t come close to the existing wall if it has been retrospectively cavity filled (average u value of 0.6). In order to have complete confidence in the installation, an insulating layer must be provided.

Extending the rafter feet without using insulation will do little to improve the overall u value as the air void will be full of cold air, thus apart from the aesthetic improvements it’s a pretty futile and expensive task.

Lambda for PVUE profile, 0.06, lambda for timber (white Spruce at Moisture content of 12% 0.13), lambda for concrete block 1.3.

The soffit should be cut from a 100mm wide profile and is shaped around the window reveals and either inserted into the starter trim (if being used) or can be pinned or screwed with stainless steel fixings into the timber backboard, at 600mm centres for white, 450mm centres for woodgrain profiles. Solid PVCU-e is more costly than the fluted hollow soffit (roughly twice the cost, and is far more robust, and easier and faster to fix for an experienced installer).

The fascia of your choice is fixed through the insulation and into the backing board with stainless steel screws. The fixing centres are dependent on the plastic profiles being used. 600mm centres, double fixed for white, 450mm centres double fixed for woodgrain profiles, 300 centres, double fixed for black profiles (these may vary for according to the profile manufacturers). The fixings must be capable of withstanding any imposed loadings, and must achieve a minimum 30mm penetration into the back board, thus with 25mm insulation and 16mm PVCUe fascia a 5mm x 75mm stainless steel screw should be appropriate. The screw heads can then be capped with an appropriately coloured head.

For further information on the installation of plastic soffits and fascias refer to :


Generally the sarking felt at eaves level will be perished and will need to either be replaced, or have a rigid tray known as a felt support tray fitted. The head lap of the eaves tray goes beneath the sarking felt and channels any excess water into the new gutter system. If the felt is rotted beyond the first tile, this is a good opportunity to replace it whilst the scaffold is up. The cost of replacing the first line of sarking felt is around £25 per metre, so on the average semi-detached house less than £370. It is advisable to install an eaves ventilation system to comply with current building regulations, which stipulates that in most situations 10mm continuous ventilation is required to prevent the build-up of condensation in the roof void, which reduces its thermal integrity and can accelerate deterioration of the timber roof members. The ventilation can be incorporated as an over fascia vent. If you have profiled rather than plain tiles it is also good practice to fit bird combs which will prevent vermin, birds and large insects making a home in your roof void, providing you are not preventing the entry of bats to an established roost. If you are plagued by squirrels, bird combs are largely ineffective as the squirrels will happily destroy the plastic barrier, making short work of it with their chisel like teeth.

The gutter should be fixed lastly. The outlets are placed in position and then one bracket at the end of the run, lining in subsequent brackets a no more than 1 metre or 800mm (as per the manufacturers fitting specification),  intervals using a string line or laser. A fall of 25mm over 16m is generally adequate. A good fall will help the gutters remain clean with the minimum of maintenance. The brackets should be double screwed with stainless 25mm x 4mm screws. The gutters are then cut and clipped into the brackets, allowing for a 5mm expansion at each joint. The Ogee gutter profile takes up to 1.7 times the flow of a half round gutter, and is generally adequate to discharge the water from the roof area. Don’t be fooled by companies which charge exhorbitant rates for the inclusion of aluminium guttering systems. They don’t carry a better manufacturer’s guarantee than quality plastic and are in the region of 8 times the cost. If you have a later problem, repairs are expensive and can’t be done by your local builder. Leaf guards can be fitted to any type of gutter if required.

Where a joint is to be made to an adjacent property (generally you are under no obligation to reform a connection if they have a rainwater outlet and there is no hard or fast legislation to prevent you from forming a stop end), the best method is to form a box from the plastic profile using a hydrophilic (expands on contact with water) seal to form the junction between concrete gutter and new gutter. It is better to use a gutter joint fixed, rigidly to the box as it won’t deflect under pressure from the hydrophilic seal. Lead linings from adjacent properties must be dressed into the gutter union. This can be achieved by removing the gutter union seal dressing the lead into the union over a 2mm hydrophilic seal, applying a further hydrophilic seal over the lead, and fixing 75mm long piece of the plastic gutter profile over the lead, and clipping in place with the bracket clips. Bituminous or epoxy liners must be detailed to accommodate the new guttering at all abutments.  Rainwater down pipes should be fitted and sized appropriately, with brackets at 1m centres, again fixed with stainless steel 5mm x 50mm screws.

Cut off method 2.

This is a cross between complete removal and the cut off method 1. It is only applicable to properties which have lintols above the windows.

The first 3 rows of tiles are removed and the concrete gutter is cut off in line with the inside  of the cavity. The rafter feet are them extended to project beyond the external face of the brickwork. The rest of the method is exactly the same as the total removal method.

It is only applicable where there are lintols to the window heads so damage to the internal ceilings cannot occur. It is more expensive than the first cut off method and is usually only applicable as part of a major refurbishmentproject.

So, what should you pay?

Given the regional variations in labour and scaffolding costs of around £200 – £220 per metre for all white installations, £210  – £230 for wood grains (due to the additional cost of materials) or black installations, so around £3600 for an average semi-detached property with 2 eaves (16 linear metres) in white. If you have a larger property you may be able to benefit slightly due to the economies of scale. Each property must be priced individually.

That’s for a top quality job with top quality materials. A good team of two operatives with the right preparation and organisation, can complete all the work within 2 – 2 and a half days on an average semi-detached property.

If you need a party wall surveyor, you can expect his fees to be around £65 to £400 or more if the issue can’t be resolved amicably, however if a civil law suit is brought against you, the judge can award for distress, inconvenience etc, which can amount to thousands, so better to let the surveyor deal with the matter under the Party Walls Act were costs are limited to the physical and the measureable. Again, I must stress that it is unlikely that you will incur any costs if you reach an amicable agreement with your neighbouring property owner and he signs the notice to allow you to proceed.

So now you know more about concrete gutter replacement than your average sales rep, the majority of installers and their surveyors. I haven’t come across a single contractor who completes the work to this specification, that’s because they don’t know how to do the job properly, haven’t thought about or understand the impact of the u value and insulation, or are too interested in lining their own pockets. It doesn’t matter how long someone has been doing a job, it doesn’t mean they have been doing it correctly.

For example, look at how standards such as the Approved Documents to the Building Regulations have changed over the past 20 years. If todays Approved Document Part L had been around in the 1950’s concrete gutters would never have been used, and your walls would be keeping you warm as toast.

Good luck with your project.