Paulgwat

Hi all, I am hoping someone can sanity check my thoughts here, we are planning a 4M x 4M sunken garden area in our self-build. Due to the plot layout and height differences versus other properties we would overlook other gardens if the seating area was at garden level. Digging down a metre means we are already in heavy clay so a soakaway isn’t an option. I am trying to get my head around the sizing of a sump and pump for the sunken area as all of the off the shelf solutions I have found seem to be aimed at large basements where any amount of water needs to be contained and removed urgently, lifted many metres vertically and cost ridiculous sums of money given the context. From a bit of googling it seems that 1mm of rain falling on a square meter is 1 litre - for Bristol, where we are, typical rainfall amounts are 0.5mm to 4.00mm per hour with storms reaching 45-50mm /hr Taking the worst case 50mm per hour and our roughly 16sqm sunken area is 800l/hr of rain fall. Given that I am only going to be moving this water about 3M horizontally and less than 1M up (there is a handy storm water drain near by that I can connect into) I am planning on using a 24V submersible pump capable of something in excess of 3,000l /hr pumping @1M vertical as these are commonly available for boats and seems to me a good margin versus expected use and the cost differential to something smaller is negligible. I am using 24V DC as the house has Loxone home automation and we have plenty of 24V already available locally to where the pump will be located So my question is how big should I make the reservoir the pump sits in? Rather than buy some huge tank and putting in perimeter channels I am thinking of using this https://vodaland.co.uk/collections/300x300-catch-basins-and-gullies - nominally it is about 25L capacity but with a couple of spacer rings that can be increased to about 45l quite easily At 4mm/hr it would take about 5mins before there was sufficient water in the catch basin to turn on the pump which would then run for about 10 seconds then wait another 5mins for the catch basin to refill and so on Even at 50mm/hr rainfall the pump would run for about 20 seconds per minute which is well within its specification. I am not too worried if a sudden huge amount of water was to overwhelm the sump as I won't be out there getting my feet wet when it does!!! Am I massively over thinking this or would you do something different? Thanks Paul

@Nickfromwales thanks, I have gone back to Potton for them to review the drawings as have had to put the scaffolding back up to look at this and don't want to have to do it again

Hi all, I am looking for some help in understanding where i might be going wrong here. We purchased a Potton timber frame and they supplied the attached detail for how the roof should be constructed for the 2nd floor (these are bedrooms and bathrooms with a wall height at the edge of the room of 1.5M and a sloping roof until 2.4M). We have followed the drawing, installing the counter battens as indicated on top of the sarking board and then installed the vapour barrier (Rhinovent Pro) over the top of the counter battens with the 10mm droop as indicate in the install instructions for the membrane. Battens have then been installed on top of the vapour barrier to allow installation of solar panels and roof tiles. We are basically revisiting this as we have issues with water somehow getting in either via the Velux windows or through the membrane itself (to our knowledge there are no rips or tears in the membrane) and running down the sarking boards and finding its way to the wall plate. So my questions are 1. Have i bought a rubbish membrane? What should I use instead? 2. Detail from Potton calls for Kingspan Nilvent (or similar) but all of the information on Nilvent says it should be laid on top of the sarking board and not over the counter battens - which takes precendence here? 3 Does anyone have specific information on how to install a velux window on a sarked roof with counter battening, as we couldn't find anything. I am sure I have left out a bunch of relevant info, so apologies in advance if i have omitted anything important. Thanks in advance Regards Paul