Window Sill Question

S

Shorty69664

Registered User
Messages
22
Hi All,

Quick question on window sills.
On a window that requires a 7' sill, my blocklayer has fitted two 3.5' sills instead of one 7'.
There is a gap of a couple of milimeters where the sills meet in the middle.

Is this OK or should I get it replaced with a full length one?
Or can you fill the gap between the sills to make it good?

As always, Any advice is greatly appreciated.
 
This is normal enough as a 7' cill is heavy. They can be difficult to bed in level as the weight compresses the mortar underneath.
The joint can be filled with a mastic or silicone that can be over painted. If it is a limestone or granite (replica) cill you can get products that match the cill finish.
 
i have a saying that if it doesnt look right to you then it more than likely is not right!
I am in the business of snagging houses and if i saw that it would definetly be on the list. It is never wise to join 2 pieces of anything together as there are potential problems in the future e.g. electric wire, pipes etc.
 
Thermalcrete, while I agree with you on minimising joints in so far as possible with a build, the difficulty arises with concrete cills weighing approx 13kg per foot for a standard cill and up to 22kg per ft for 100mm deep face cills. You can see the potentials firstly-lifting, shifting and manoevering a 7' cill and secondly (and more importantly) ensuring a continuous mortar bed and watertight seal to the base of the cill.
Once the DPC is not jointed this practise is accepted.
 
Re: Window Cill Question

Thanks for the replys guys.

As this is normal practice and causes no problems, I'm ok with it.
As always thanks for sharing the knowledge!
 
Additional cill question. My cills sit solely on the outer leaf, with a 1" gap approx between the rear of the cill to the inner leaf. My blocklayer wants to fold the DPC over the back of the cill and infill with concrete. However, practice seems to indicate that a layer of 1" insulation should be placed between the infill and DPC. I am worried that the "bearing" weight of the windows may over time loosen the cills if insulation is used. Any advice would be appreciated.
 
Put in the insulation, otherwise you have a thermal bridge. The window doesnt bear on the cill. Windows are fixed with straps to surrounding blockwork.
 
Dugsy said:
Additional cill question. My cills sit solely on the outer leaf, with a 1" gap approx between the rear of the cill to the inner leaf. My blocklayer wants to fold the DPC over the back of the cill and infill with concrete. However, practice seems to indicate that a layer of 1" insulation should be placed between the infill and DPC. I am worried that the "bearing" weight of the windows may over time loosen the cills if insulation is used. Any advice would be appreciated.
Click to expand...

as joker say, definitely put the insulation in.... if you dont you are not constructing in accordance with building regs (most probably) and best practise...

if you have the space id try to include thicker than 1"...
 
Redundant, so have the time to do the infill job myself. Can anyone advise as to the mix required for the infill, sand + cement, or should chip be added as well. What ratio of mix?
 
A window does sit on a cill, it is strapped at the sides to keep it upright and in position. Usually a run of silicone is put on the upstand of the sill to give an extra sealant between the window and the concrete/stone cill
 
I have seen cills joined in very old houses using lead which I presume was melted and poured into the joint. The joints are still as good as the day they were put in. I suppose they had no silicone back in those days
 
you may use foam spray for make perfect sill. But the gap is too small so it may become costly for you. The final choice is your.
 
scon home, it is possible to lift sills of this length - i recently fitted a 6' sill on my own and positioned it 4' from the ground. I owuld not recommend doing it by self but did not have anyone around at the time. 2 people will easily lift a 7'sill. Weight is not a pronblem with the mortar either. Definetly need to put insulatin behind sill as a cold bridge will otherwise occour. The weight of the window does sit on the sill - that is the concrete sills job! Definetly put a layer of sealant on the upstand of the sill to bed the underside of the window frame to the sill so as not to allow an air gap as cold air will come into the building and heat will escape
 
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