Saul

it wasn't my architect and didn't think you'd need one for a simple garage. Have now got a designer working on it which is costing £600 that I'd hoped not to spend.

I didn’t draw the upstands. They would border around the front and sides 150m above the top of the front ferring but the back will be open to the gutter. Proper drawings are being done. This is just me playing on Sketchup.

architect says that the eaves height of a flat roof is measured at top of roof, ignoring the parapet which would sit above the top of the roof from the Government Website http://data.parliament.uk/DepositedPapers/Files/DEP2012-1435/Parapets.pdf For the purpose of measuring height, the eaves of a house are the point where the lowest point of a roof slope, or a flat roof, meets the outside wall. The height of the eaves will be measured from the ground level at the base of the external wall of the extension to the point where the external wall would meet (if projected upwards) the upper surface of the roof slope. Parapet walls and overhanging parts of eaves should not be included in any calculation of eaves height.

architect says that the eaves height of a flat roof is measured at top of roof, ignoring the parapet which would sit above the top of the roof

Upstand requirements for flat roof design IKO TEAM 09/01/2022 A frequently posed question when designing flat roofs is “What upstand height do I need?” On the face of it a simple question with, one may think, a simple answer. Most of the time the simple answer is “150mm above the finished roof level”. We may give that advice but unless we probe further can we be sure that the advice is fully understood and correctly interpreted? In our experience, not always. BS 6229:2003 ‘Flat roofs with continuously supported coverings Code of Practice’ and BS 8217:2005‘Reinforced bitumen membranes for roofing Code of Practice’ both state that if unwanted water ingress into the building is to be avoided all weatherproofing upstands occurring around the roof area; (which would include abutments, rooflights and service vents etc) must have a minimum height of 150mm.

I forgot the 240mm I Joists from the list summary. The joists will run Side to Side so no need for a Steel. The door mounts to the face of the pillars inside. The Door is 2000mm tall but the running gear internally will be 140mm over the height of the door. Apparently the upstands don’t count as Roof Height so I should be able to do this in PD at 1m boundary.

Would love to get advice & thoughts on how a serious issue might be appropriately resolved. Lab tests have just confirmed that M4 mortar has been used below DPC on my house. Further to this it appears the DPC Membrane has been laid quite far back ie it is recessed from the face by about 25mm. This will presumably cause bridging, especially with the sandy M4 mortar and therefore result in rising damp. The DPC has been laid in rough face bricks rather than engineered bricks but they are classed as S2 F2. Feeling anxious and worried. The house is rendered Block above DPC. Thank you

Looking for any final advice before I move forward! Thank you! I’ve now moved in and need to get this garage built asap. It’s looking like it’s going to cost £35k all in which is still a massive amount of money. My issue is now with the internal ceiling height I’m like to get being 6’2” tall and thinking internally it’s going to be under 7’ To get this garage built within permitted development I will be GIA under 30m2. Garage Width will be 5.5m and Length 5.8m Externally. Block Built with Piers and Rendered to match the house. Maximum height under PD is 2.5m. The Double door will be 4500mm wide by 2000mm tall so I only have 500mm left!! The Headroom needed for the Door is 140mm. For the flat roof I need at least 240mm tall I Joists for the width span plus I need Ferrings and then a Stand Up 2500mm Max Height 2000mm Door Height 140mm Door Mechanism Head Room 78mm Ferrings Height 150mm Stand Up I’m over already by 88mm This is crazy!

Will do though not sure I can manage the weight of 5.83m long standard wood joists. I'll most likely go standard I Joist and Ferrings. Not seen anyone sitting I Joists on top of the block work or if they have how these would be secured to the blockwork...perhaps upside hangers. The house has Web Joists sitting on hangers within the walls but don't want to do this for the garage as would need another row of blocks and not keen on that design for something that doesn't have a floor above it.

Presumably you would add one firring per joist. Just found a site where they are £3.25 per m up to 6m. For my build with 5.83m this would mean 15 x 5.83 x 3.25 = £285. 2 rows of bricks on one side of garage would be around £50 excluding laying labour. I don't like the idea of offset walls but don't know why that wouldn't work unless there is a stress issue on the I Joists from not being square if they were ever subject to heavy load from snow etc. At the same time at the high end of the firring ie 150mm above Joist I'd prefer to know that the OSB was attached to the joist where in reality it will be nailed to the Firring which will be nailed to the Joist. The wall ties won't offer any protection against wind strain. Who would have imagined that 3 walls, a floor, a roof and a door could be so involved!

Thanks. I've pretty much abandoned the idea of a gutter at the back of the garage. As clean as that would be I'm not putting a steel across a door gap that wide as it will be super expensive. The issue with a 5.83m Firring is that it would be approx 150mm down to Zero. I just feel that those would be impossible to cut consistently.

I have read all the previous chains on flat roofs and know pitch angle and methods has been covered to some extent already but trying to wrap my head around why you would use Firrings as shown in the first picture when you could just create I Joists that have a slope manufactured within them ie by cutting the OSB Web such the bottom edge is flat and the top edge is sloped. In effect the I Joist would then have one end being 450mm tall and the other 300mm tall overall. (I know in the below example I have run Firrings front to back. If I used them this is what I would do as would rather have the gutter at the back) As well as custom angled I Joists I know I could also build up one side wall to be taller by adding a row of 2 bricks which would achieve the same fall off with guttering placed on the side of the garage rather than the back. I just don't like the gaps that this creates and think an angled I Joist allows everything to be nailed together square. As this is a single skin 100mm Block 7.3 build with Piers and no heating it won't be insulated and will simply have an 18mm OSB roof with EPDM Rubber, Fascias and Guttering. STS board will be attached the timber work and the sides will be rendered. Roller/Double Door. Appreciate any comments. Ultimately I need to build this as cheaply as possible as people seem to think £45k for a double garage is normal. I want to achieve this for max £20k in total including base finished and ready to store my classic car. Cheers Saul

So looking like this will now be a Block Build Garage Rendered in Weberpral Monocouche to match the house. If anyone knows of a good building company that might want to take this on in the Bicester/Oxfordshire area any recommendations would be appreciated. Plot shown as per attached.

£28-45k. Happy to do quite a bit myself internally and have an electrician father but definitely want the water tight structure handled by pros. Best of luck finishing yours. looks like great fun!

I am aware of them but put off by negative reviews and wondered about it's strength as they look more like posh sheds. Over a Double width door I'd be a little bit scared but am sure yours is fine especially with the shelter from the wall next to it. Good luck with the door!