Chimney capping cost
For most people accessing a chimney stack safely themselves will be a daunting and potentially dangerous task, but it you are competent with heights read further down for DIY fitting instructions and you could save a large chunk of the chimney capping cost.
The common average cost for chimney cap fitting that I would charge with easy access, would be roughly £150 to supply and fit, or £100 or just under if the customer supplies the cap. The labour charge is the same for multiple caps on the same stack.
You can sometimes save a little money by buying a chimney cap for a roofer, builder or chimney sweep to install for you, and it can work out cheaper for you and easier and quicker for the installer. Often when I’m asked to cap off a chimney or install roof cowls, one thing that will make the job more expensive is the two visits it takes to first assess the job, then order the cowl or cap and turn up again for fitting. This can either make it disproportionately expensive or reduce my profit (I don’t like the latter). If the customer had already ordered their cap or cowl it would be a simple turn up and fit procedure, which saves time and money for both parties.
How to cap a chimney off
There are many times when a chimney may need to be capped, like to stop birds getting into the chimney pots, stop rain blowing down the flues, detecting and stopping chimney leaks, or to restrict heat loss from a redundant open flue. In this article I will show you the best methods from the totally free to the low cost DIY and professional installer options, as well as…
- Find the correct flue – How to determine which flue is which on multiple chimney flue stacks, and smoke test.
- How to measure chimney pots – Done from the floor with no special kit.
- Best chimney cap – Which is the best chimney capping method for you and product links provided.
This video on chimney flues runs through the process of chimney flue and pot identification so you know which chimney is which, as well as smoke testing and how to measure a chimney pot for inner and outer diameter.
How to determine which chimney flue needs capping
If your home is a basic one fireplace / one chimney pot affair this will obviously be a simple matter, but a lot of homes will have 4 or more chimney pots that serve 4 fireplaces, some of which may be blanked off, bricked up or unused. As a rule of thumb taking a common semi detached home using 4 chimney flues as an example, normally the two outside chimney pots serve the downstairs front and back room fireplaces, and the 2 inside pots would be used by the upstairs fireplaces that are commonly bricked up or unused.
Flue construction – This is an average terraced house, semi detached or detached construction in the UK. Please note this is just a common example for educational purposes, checks should always be made to verify flues.
External chimney pots – Here you can see how the chimney pots connect to their corresponding flues and in turn to the fireplaces. This example is a 1930’s semi detached, the neighbour’s pots can be seen in the row behind.
Warning! Safety first
The information above is a general guide for help and guidance and may not be correct 100% of the time, blocking or restricting the wrong chimney flue can be fatal. Always test chimneys and flues with a good quality coloured smoke pellet first to be sure you are working on the correct chimney pot.
Smoke test – A simple cheap smoke test will rule in or out chosen chimney flues easily, smoke is drawn up any open flue and it can be seen from outside easily as long as the wind isn’t blowing too hard. A second person filming with a smartphone can be an excellent reference at a later stage.
How to determine chimney pot size
If you can accurately guess the size or width of the chimney pot from the floor you can order the right cap or cowl one online. The good news is this is relatively easy once you know the rough size of a house brick and the thickness of the walls of a chimney pot.
Chimney pot width – This is a very common standard plain buff chimney pot, here it has an internal width of 9″ (230mm)
Using either the naked eye or a set of binoculars get a ‘side on’ view of the chimney pot you wish to cap or cowl, then find a full sized brick nearest to the chosen pot as a reference, normally directly underneath. Now imagine that the brick is placed on top of the chimney pot itself and make a mental note whether it would fit inside, hang over, or sit flush. It may sound silly but once you know that the width of an average UK house brick is 225mm ( 9″ ) for imperial or 215 (8 and half “) on a modern property, it provides a very accurate impromptu tape measure. See brick sizes here… Common brick sizes.
Chimney pot internal dimensions – The two most common sizes are 8″ internal and 9″ internal. Pictured here is a common chimney pot and an older imperial measurement brick, as found on most pre – 1960 properties.
The other factor you may need is internal pot size, this can also be guessed quite accurately if you know the average thickness of a chimney pot is about 25mm (1″), simply factor this in and you can work out most chimney pot width’s quite accurately. Obviously if you have large decorative rolls on top of the pot, make an allowance for this by guessing, using a brick as your guide. (also see picture above).
A game of ‘I spy’ – This is just for fun or practice, like the sado’s version of ‘I spy’. Two chimney stacks viewed from the floor without binoculars and both built with old imperial bricks, one pot has internal 8″ and one 9″. You should now be capable of working out which, I have photo shopped bricks from the stacks above the pots to help.
How to cap off a chimney
DIY Chimney cap installer – This video on chimney capping lists three very common methods that are easy to fit, and easy to take off again when and if you need to.
The best chimney cap
If you’re looking for a good long term solution to capping a disused chimney its very hard to beat the C-Cap in my opinion. Its a relatively new solution to a professional quality chimney capping product and comprises of a tough Terracotta or Buff coloured waterproof plastic dome with built in insect filter and air ventilation. Available in two sizes it simply clamps inside the internal cheeks of the chimney pot with sprung loaded wire clamps and is fitted in seconds, it can also be used where the chimney pot is flush with the surface of the flaunching making it one of the best chimney capping solutions on the market. If you spot any large visible cracks in the chimney pot that may cause damage to the pot via the internal pressure of the spring clips, check out the alternative metal capping method below.
C-Cap – Fast fitting, no fiddly jubilee clips, keeps the rain and birds out, ventilates, has insect filter and is 100% waterproof.
C cap sizes and dimensions
Here are the two sizes available for C caps, just in case you require exact measurements for internal or external dimensions for a chimney pot.
Cap for most sizes – The standard size C cap gets used the most because if fits the most chimney pots. Compresses to just less than 8″ (200mm) with relative ease but sits tight all the way up to 11″ (280mm)
Metal disused chimney capper
Another excellent type of Chimney Capper when capping off disused chimneys are the metal versions with inbuilt fixing straps and a large stainless steel jubilee clip. Again mostly available in Terracotta but sometimes in Buff, there are really two typical versions of this, a plain cap which can be adjusted in height slightly on the pot to give varying amounts of ventilation depending on your preference. Alternatively they can have a built in bird mesh where the ventilation is a set size, in a similar way to a chimney cowl. This method of strap and jubilee fixing used isn’t practical if the chimney pot top is flush with the flaunching, but is excellent if you have any visible cracks in the chimney pot as the straps clamp the pot together.
Metal chimney cap – One big plus of the metal strapped chimney cap, is that the strapping and jubilee fixings can sometimes be adapted, or modified to fit chimney pots that may have a strange shaped top or awkward angles or flutes. Grill mesh vented versions are also available to give more ventilation without bird entry.
Chimney cowls for capping
Chimney cowls are normally used to adequately ventilate chimney flues connected with an appliance like gas fires, open flame gas fires, wood burners, coal fires etc. However a Standard Chimney Cowl can provide a good alternative to capping a chimney, or if you think you may use the flue later to connect an appliance. Chimney cowls can be bought for a specific type of fuel or even as a multi purpose Multi fuel cowl like this.
Chimney cowl – Keeps rain, birds and squirrels out, ventilates and keeps the flue dry, also available in multi fuel if required. However it will not be as thermally efficient as a standard chimney cap that uses trickle ventilation if this is a concern.
To see more chimney cowls, fitting and what common problems they can cure see my webpage on chimney cowl installation.
How to Seal a chimney
One old and virtually free method of capping off, or sealing a chimney that is generally no longer used is to make a lead cap. These can simply be made out of a scrap or an offcut of lead, beaten into the correct shape and bonded to the top of most chimney pots to effectively seal it and make it waterproof. The reason this really isn’t used anymore is that sealing the pot to make it water and air tight can cause internal condensation, especially if the flue is open inside the property. If this is the case warm moist air may rise up the inside of the flue, condensate and drop back down into the property or create dampness in the brickwork of the flue itself, possibly showing itself internally at a later stage.
Home made chimney cap – On the positive side, as a purely temporary measure for the purposes of leak detection or elimination, say for suspected leaks caused by direct rain entry into the flue, or to keep out nesting animals it can be a very handy quick fix, especially if the chimney has ventilation already built into the stack.
The pepper pot clay chimney cap
Another chimney cap worthy of note is the fired clay pepperpot, this is a traditional drop in solution to chimney capping, and on the plus side one size fits nearly all. On the negative side the mating surface underneath the pepper pot are best sealed with silicone sealant, as rain tends to roll over the domed surface of the pepper pots and leaks can be worse after fitting than before if this isn’t done. And of course they are heavy, will break or chip if dropped, and can be a lot more expensive to buy and ship.
Chimney pot removal and capping
I’ve got to be honest, this would be my least favourite form of chimney capping unless the chimney stack needed reduction in height, or the brickwork corbelling had become unstable. Firstly it’s more work and therefore more expensive to do, secondly if you change your mind later on, or sell your house this may involve another costly re-build to undo the work later on (chimney pots aren’t cheap these days either).
Chimney pots removed – I see these everywhere unfortunately, and quite often they leak internally one the mortar between the slabs wears or cracks.
If the top of the chimney is capped with building slabs, as is often the case rather than flaunched, or fitted with a concrete cast top, it risks leaks down a flue where slabs have been joined together. Ventilation in the form of air bricks should also be fitted into the brickwork near the top of the stack to stop internal condensation. Pretty it isn’t.