Getting guttering square to the fascia can be a problem. If the fascia is not perfectly vertical (and many on older buildings aren’t) then when fixed gutter brackets are attached they either need to be packed to make them square or, more commonly, they are left at odd angles either sloping into or away from the wall.
This can cause problems in heavy rain showers. If there is any slight blockage the gutters don’t work as they should and can easily overflow either against the wall or over the outer edge and then to who knows where. This can be a major cause of damp in a house.
Packing the bracket will probably work in the short run, but if the packing falls out this can cause even more problems. So, a sustainable solution.
We deal with Lindab guttering and they offer an Adjustable Snap-on Bracket (Code SSK). These are very similar the normal fascia brackets, but rather than being solid metal they have an adjustable metal arm that clots into a grooved receptor and this gives a wide variety of choice to get the guttering square to the fascia. So effectively they twist the guttering into shape to give the best result in ensuring that the gutters run true.
So if you are concerned with the angles of your fascia it is worth stipulating adjustable brackets rather than then fixed ones. If you think that you might have some issues with the fascia then I would go with a 50:50 mix between the two. Cost wise they are similar (adjustable slightly more expensive), but it could save you a lot of headaches and hassle when fitting and living with a new system on an old building.
I have also been informed of the following that might be of import to your particular project –
In order to use the standard fascia bracket (KFK)
you really need to be able to snap the guttering in at the back. If the
existing roof overhangs the fascia this may be impossible. When you are
on a ladder it is difficult to get the gutter to snap in at the front
due to the strong rolled edge. In this situation, even if your fascia is
vertical, you need the adjustable fascia bracket (SSK) because the
guttering can be placed into it underneath the existing roof and the
bracket has a snap-on front clip. Not all of the suppliers stock both
kinds, and the Lindab literature does not seem to explain the problem!