Finlock concrete gutters

Finlock gutters were commonly used during the 1960s and are very much of their time and in most cases are now past there time as well. We come across them every now and then when we do a building survey and rarely if ever are they in sound order.

The gutter system was manufactured by a company called Royston to a range of designs – all broadly similar, but with some changes to the detailing, intended to be a combined cavity closer / lintol / and gutter system to speed up and simplify construction. The system comprises an integrated concrete gutter, lintel and eaves product that is fitted in sections which are typically 200mm to 250mm width incorporating a cavity closure at their head (see diagram below).

Finlock gutter system diagram
The Finlock gutter system.

These are fitted to the top of the cavity and oversail the outer face of the wall forming the gutter. Where they pass over window openings, there is a lintel tray into which the lintel sits or one is cast. Within the gutter trough a waterproof coating is applied.

Problems with Finlock concrete gutters 

Common problems include:

  • An inadequate number of outlets which causes flooding and leakage.
  • Gutters have often been lined or sealed with an asphalt or similar liquid applied product – older repairs have very often not only failed but worsened the problem as the finish is crude and uneven and the channel size has been reduced and so has capacity.
  • Gutters are generally laid level and are consequently extremely liable to blockage and flooding, over time the sections settle and become misaligned making this situation worse.
  • As sections settle the joints opening up and can start to leak, this leakage can become apparent on the inside of the building.
  • One also sees vertical fractures internally at around 240mm centres where the inner edges of opened up either by settling or usual thermal movements in the building.

There is a problem with Finlock gutters when windows are replaced, particularly when the windows are replaced by operatives inexperienced with this guttering system as they often do not realise that the gutter also forms the lintel. Typically they failed to provide adequate support and consequently misalignment can develop when the old window is out and before the new one goes in.

Condensation and dampness becomes evident internally typically to the upper 200 mm or so of the wall. This develops as a result of a ‘cold bridge’. Quite often Finlock gutters were used above cavity walls which were insulated or had better thermal performance.  The concrete gutter is solid from outside to inside and so when it is cold outside the concrete sections are colder inside than the adjacent surfaces and so attract condensation when environmental conditions are right.  This can often be seen as a line of black mould just below the ceiling.

Repair can be carried out, essentially it is a choice between lining the gutter or cutting away the protruding section of gutter and fixing a more traditional fascia board and gutter. Both methods have their benefits and will work, on balance we prefer to see them cut away rather than lined because that helps to relieve the condensation problem.

In the gallery below there are some diagrams of the system and some pictures of bungalows in Hythe, Kent. One can see typical gutter details as well as a bungalow where the gutters have been cut away and replaced.

Need a survey, homebuyer report or just need to talk gutters and problems?  Give us a call 020 8295 1200 or complete the quick response form below – if you want us to call you please add your phone number.

(Originally published by Steven Way, 6 February 2012)