Gus Potter

Well done you! Keep us posted.

As purely an observation. Many posts on BH relate to BC / Planning and in the round tend to take, let's say.. a disparaging view. In my day job as an SE I often get phone calls about this kind of stuff. Many calls go along the lines of.. Gus can you give us a report that says it's all ok. In particular we would like you to say by all Ok we mean.. everything is ok.. structure, insulation , condensation control etc! We would love you to say this as we want to maybe get lending and later on when we come to sell we need your paper work. But to report (and for my PI to cover you and I) I need to know if there is anything that is going to compromise say timbers.. hence I need to look at say condensation risk, weathering details and so on. I could of course say.. the structure is fine.. but caveat, as I must do, to protect myself.. and then the lender will ask for more detail. We end up back at square one. Nick. In technical, insurance and SE reporting terms this needs clarification. Most of this stuff is designed for a 50 year life span. SE's design on the probability of the maximum load occuring over a 50 year period. It is fool hardy to say if after 20 years it's going to be fine going onwards as the structure may have not been fully loaded up yet. In the next 30 years it may be subject to the full design load. This is the difference between someone like me that is going to have to carry the can if someone gets hurt later, or a claim is made and someone who has lots of experience.. but only 30 years of it! This is not an abstact concept. An easy example is say a loft conversion. You have a kid.. they grow up to be a rugby prop, they ask their mates round to the attic room, they party, there is a bit of "dynamic" loading. Very quickly you can exceed the design load and eat into the factor of safety. Another is snow loading on a roof. Now over the last decades we have not had lot's of snow. But the climate is changing. The air can be warmer, the cold fronts more defined. The risk is that we get a heavy dumping of wet and heavy snow that traditionally would blow off a roof to some extent. Wet snow just sits there. I base my SE judgements partly on the experience of SE's and Civil Engineers over that last 200 years (often more that) which have been woven into the modern design codes we use today. This then allows insurer's to write premiums and banks to lend. Now insurers understand how SE's approach risk and vis versa, the probability of failure and where they can seek recourse to say an SE's policy. Probably the thing you should be concerned with most is to ensure it is not going to fall down or later the structure start protesting. Really!

Ok I'm going to give you the benefit of the doubt here. No photo as it's dark o clock! I might be able to reassure here, but not promising anything. If you want hand sketch what you have on A4 paper, photograph and post. Show a plan view and annotate the depth to the bottom of the trenches you have dug relative to the highest finished ground level 0.000 m . If the ground is sloping mark the highest ground level as 0.000m and then assign values to any ground that is lower. Also show you main house founds. Show all foundation widths, mark the plan dimensions to the outside of the masonry walls and the outside edge of the foundation. Confirm anything you are placing on the founds is single storey. Provided that the highest part of the found is on competent ground then an extra 200mm is unlikely to result in excessive differential settlement. All parts of the house will settle differentially due to variation in loads, depths and soil variations, SE's design for this. The most common problem is folk leaving a soft layer where everyone has tramped about, essentaily laying the concrete on a slurry. If you are stepping the foundations then make sure the mesh extends over the step.

If you have corrugated steel profile roof sheeting something like this may be more suitable for the weathering detail. Your air tight layer is further into the depth of the roof. The issue is sequencing of the build process. Weather proof steel sheeting is probably going to go on first before you start to introduce plasterboard and air tight layers. You probably need a second flashing to pipe gizmo that you can bond to your air tight layer. Your air tight layer is usually a plastic membrane so we need something that you can use to bond the plastic to the soil pipe. Remember that soil pipes expand and contract a bit when you empty the bath warm water for example, thus we need something flexible. Can we just rely on air tape or do you want something more " professional" looking. Like this:

That looks a good theory.

Ok that works if you have an eaves and ventilated ridge with a 50mm air gap. Slate hooks are a nightmare, and dangerous for folk going onto the roof to maintain it. As part of HSE stuff you design to make sure, say in roofs, you don't have exposed sharp nail heads, slate hooks are nasty and are a puncture / trip hazzard. Why not just do the job properly? Slate hook are more associated with remedial works.

Hello all. I've started a post but ties back to @Digmixfill Sometimes (often) things are not level etc or we have a complex roof shape with lots of different angles framing into hips that need some support. This, even for the experienced, can be a challenge to visualise itnever mind build it! Then you need to find someone with the skills to actually do it. If it looks hard then they will hike the price. When we have to check / chamfer timbers / do 3D cuts, particularly large ones then if the joiner makes a mistake then they often have to pay for the wasted material. Cutting joints in the rain or techincal ones just adds risk and stress. Below is a design where I'm trying to reduce the risk and help everyone visualise what needs to be done and the sequence of the work. Below is a 3D model to help eveyone see what we are trying to do. The roofs are at different angles and so are the hip rafters. The red bit is the main padstone support. Below is what the rafters and hips look like in 2D on plan. I try and name things to help everyone easily identify what parts of the roof we are talking about. In true technical drawing terms I you don't need to be "so chatty" but it avoids confusion. Some of the dimensions are used in my structural calculations so are not actually "Architectural" in purpose. I put gridlines on things. I still amazes me why "Architect's" don't do this, even if they hide the layer for visual Client presentation. It's just stupid in this day and age not to. It makes it really hard for SE's to line up floors for example, that wastes time which Clients end up paying for. Below is the way hip 02 connects in detail to hip 01: The edge and end distances for the fixings are critical, hence dimensioned out. In 3D it looks like this: Now here is the secret. You could try and rebate hip 01 over the padstone.. very hard to do and the joiner only get's one chance. Or you can leave the hip H01 as is and make up a seating plate for it from offcuts of timber. This way the joiner gets as many chances for free, they can make it up on the ground and you don't have to cover the risk element! To finish. Lots of this stuff is about making things buildable and if you have funny angles, things not level then coming at the problem from a different direction, always of course with a view to cost can help. No point in designing something if the money is not there!

Posts overlapped!

Hello David. Welcome to buildhub. You'll get lots of different ideas here.. the best thing is to mull them over and adopt the ones that suit you best. Lastly, excuse my spelling and grammer! You asked for thought! The following is to give you some power to your elbow, not intended to be any form of critisism, after all you are still at the preliminary design stage. Shetland eh!. My sister lives in Tiree both can be increadibly windy with driving rain. As such you really have to almost go above and beyond the normal call of duty when considering the design details, which are crutial. I'll start from the top down.. the slates. You have two choices in terms of nailing. Traditional or modern. Traditional method: In the islands for smallish slates we often go for one nail in the head of each slate then every third course head nailed and also cheek nailed. The cheek nails restrain the slates below as they have effectively 3 nails in a triangle. Now at the verges and eaves, around Velux or chimneys.. anywhere we are going to get horrible wind vortices we do one nail in the head and fully cheek nail. Now the great advantage of this is that it works! but also lets you maintain the roof for the next 60 years. Modern method.. as per most manufacture's recommendations. Two nails in the head..but the roof will cost more to maintain in the long run, likely to leak more before you spot it. There is a tendency these days to use larger slates. each slate gets more wind load and the nailing points get more stressed.. more failures. Consider the benefits of a smaller sized slate.. even though they cost a bit more to buy and fix. The NHBC, slate suppliers only guarentee for say 10 years. If a slate cracks you don't see it as it does not often fall out as it has two nails in the head! In other words.. I often suspect that the suppliers and warranty providers are aiming to reduce their liability over the warranty period and don't care what happens after that. Suggestion: Have a chat with your Architect and if possible traditional local slaters. This part of your drawing has potential conflicting information and design approaches. The slates are shown on battens and counter battens on a breathable membrane on sarking. If you go traditional then the slates get nailed directly to the sarking, no battens or counter battens. At the eaves there is no undercloak slate shown, the overhang into the gutter is short. In Scotland we often use timber sarking. Us SE's make good use of the roof stiffening effect it provides. Normally we specify that the timber sarking has a 5.0 mm gap between the boards and is no wider than 100mm. This provides suficient repeating gaps to allow the breathable membrane to function. Now you don't have any eaves ventilation shown..that is ok as you have the sarking gap. Sometimes you see the permeable insulation between the rafters going right up to the underside of the sarking. Your drawings show a 50 mm gap. This indicates that there is possible a lack of understanding. A 50 mm gap is usually mandatory if you don't have sarking gaps etc and rely on eaves and ridge ventilation. Normally what we do, and I do a lot of this as do many Architects I work with, is to leave a 20 mm gap under the sarking.. just to disperse the water gas so it reaches the sarking gaps and gets out. Now that means you can make the insulation between the rafters 30mm thicker which takes it up to 200mm. Now often we are looking for buildability and at material procurement. It just so happens that TP10 etc is commonly available in 100mm thick sheets. And what you try and do is use same sheets where ever you can in the rest of the build. Your drawing shows a timber frame. The detail at the wall head looks off. The cavity barrier (fire stop) is not going to work as fire will bypass that. The fire stop batten needs to have a panel top rail or head binder behind it. You are building in Shetland.. it's also very wet at times (likely any wet timber delivered) will stay wet so you have to be much more aware of timber shrinkage. The external walls stay pretty much still but the kit shrinks thus you need to leave a gap between the top of the blockwork and anything connected to the timber frame. This is the time to get your head around some of this stuff in case it later causes havoc with the detailing of your windows and door height for example. On first glance this means you fascia boards need to be deeper as in Shetland wind driven rain goes upwards more often than you think! Suggestion: Have a chat with your Architect about whether you are mixing and matching design approaches. It's ok to do that.. but you have to be clear about the design philosophy. Turning now to this top left part of your drawing: In Scotland in the central belt BC 99% of the time accept render on block with no cavity tray. But where you are you get not just ferocious wind and rain but persistent rain and a bit of steady wind. This is also very onerous.. watch out! I would put cavity tray over the door and window openings and dress the breathable membrane over that. They don't need to always be expensive ones. A good brickie can form up a tray with a weep vents out of a standard roll of DPC. The thermal break in the timber lintels should be further out. I would with my SE hat on omit this and if need be use deeper timbers for the lintel and lose possibly the timber frame (TF) top rail over the lintel. It's also got to do with timber shrinkage and the postition of the loading from the floor joists. In terms of insulation. You show the opening reveals as having 25mm of insulation. If you are loking for a high performance house then aim for 50mm.. but then the windows don't fit! I often use 50mm reveal (called ingoes in Scotland) insulation but to make this work we need to ask the window / door supplier to include a thermally broken frame extension kit. Suggestion: Have a chat with your Architect, ideally make contact with BC and see if they will give you some advice, hands on experience of what works in Shetland. Turning now to this bottom left part of your drawing: I'll not make any comment on the floor slab etc for now. But you'll need more of a drip on the window cill. NHBC require 40mm, the arrangemnt shown is not adequate. As it's TF you need a fire stop under the window cill and you'll need cassette vent to ventilate the timber frame cavity. Ok that is probably enough for now for you to digest. I would go back and review, learn a bit more before you spend too much time calculating in detail exact u values etc as once your SE get's their hands on this and Scottish BC you don't want to end up back at the beginning again. Hope this helps and all the best.

Ok I can see you are wanting to explore this. It's a good thread you have started as it delves into what can be possibly achieved on paper and what can actually be built at a sensible cost. Don't apologise, you are not sitting an exam here! Neither am I as I've clocked off the day job. Mortar is less forgiving in terms of movement so consider lead, even if to rule out. Yes they are. But so is PIR insulation. Below is the data sheet from Steico for thier high compressive strength insulation. And below for thier internal insulation. I won't go into detail about how SE's do the sums for compressive strength.. other than to say we do not use for example this value when designing as it squashes to much. For you the main thing is to look at the thermal conductivity of the two offerings. The higher compressive strength has a value of 0.048 W/(m.K) the lower (weaker insulation) 0.038 W/(m.K) which is about a 20% difference. If you remove the repeating bridges but even use the higher strength stuff you may get a better result. It's likely marginal.. but as I said before.. you need to look at the perimeter details, noggings etc and buildability. I understand what you are trying to achieve technically. I'm familiar with how this sort of stuff can work, the references you cite. But I can tell you it is almost unkown to be able to build this. It might be a good idea to start to produce some detailed drawings of the junctions / interfaces between the different elements. Even if you do this as a day job it's going to be demanding. All the time you have to think.. how do I explain this to a builder and what are they going to charge you for this.

Stick with lead for the skews. If you put forward an evidence based design then most accept. Like in all walks of life there is a bit of "personality" involved at times, younger BCO's and designers are, by default, less experienced in communicating which can lead to crossed swords. Client's sometimes are the same, maybe they don't allocate enough funds to the design fee element. In summary if your design is sound then BC will accept.. you often need patience. Ok I can see what you are trying to do, a few comments in line with your text which I've turned into italic. Plasterboard 50x50mm horizontal battens with 50mm wood fibre insulation batts between You horizontal timber battens on the inside introduce a repeating bridge. You can test this repeating bridge effect by using say Kingspan online calculator. I often use a continuous layer. But you need to check that the plasterboard can be fixed through the wood fibre on the inside.. it works for PIR. Intello VCL membrane Not sure about this. I would be inclined to use something impermeable like plastic. existing 150x50mm rafters, fully filled with more wood fibre batts This sounds ok in the main body of the roof and on paper. But around the roof edges, these are weak spots. leave the full fill insulation 10 -20mm shy of the underside of your ply just to let the water gas / moisture disperse. . I'm not going to to explain in great detail here but the principle of the sarking is to have gaps between the boards. You full fill is not compatible with your marine ply.. which is pretty impermeable. wood runners fixed to the inside of each rafter along its whole length Ok see that you are doing. But you have structural problems in terms of the edge distances of you fixings. 25mm marine ply fixed to runners and joists sitting flush with outer surface of existing rafters Now marine ply sounds great.. but trying to drive a long copper nail into this is not that easy.. ask an experience slater. Again it may be ok in the main body of the roof.. but you are going to have massive problems at the edges and any roof lights / service penetration. 35mm Steico tongue & groove woodfibre sarking Ok.. if you follow the manufacture's fixing detail. vapour and air open waterproof membrane Ok.. for now. ~8mm "heavy" slates with 75mm+ stainless or copper annular ring nails, two per slate centre & off-centre to prevent rotation I would not slate this way on you job, rather I would adopt the traditional route. In Scotland as we do a lot of traditional sarking we do one nail in the head, every third course cheek nailed in the main body of the roof. This lets us maintain the roof easily. Commonly in England the slates are fixed to battens. I think I can see your design intent.. but I very much doubt you can get anyone to build it dilligently. TYou design has technical flaws. In summary.. my advice is to say "I had a good go" but let pragmatism and budget cost prevail.

I kind of think back to when I first joined BH. I took me a while to get my head around how it works. BH is not like some woke Blue Sky place, but I can't really think of anyone who is deliberately horrible. @WisteriaMews post more info with lots of details as I said before and loads of folk will rally round.

Great thread this, all different points of view, appoaches and innovation going on. One could conclude there is no perfect solution... but that is the joy of design, you do the best you can.. so long as you can live with fact that there is no perfect answer. An element that flags up for me is that many posts are a personal view, some just do this as a hobby which is fair enough. Few, if any recognise, (rarely mentioned on BH) that they are just a custodian of their house which one would hope will last for more then 60 years. My mindset is... lets build stuff that is pragmatic and look at the maintenence costs over the life cycle of the building while retaining its market value. My own view is that a sealed house that relies on mechanical ventilation alone is not a long term solution as ownership and use will change over time, the systems become degraded and costs rise.. it gets worse if no one understands what you did in the first place. At last.. well done you! An OH cowl is the best in my view. No moving parts and requires no wind to function in terms of passive stack ventilation. If you want more passive ventilation you just increase the diameter.

If you want more targeted feedback then suggest you post your drawings. The key here is to recognise that folk on BH have never seen you project so rather than making them guess just provide as much info as you can. Take title boxes off drawings and identifiable marks if you wish.

It is indeed a puzzle and interesting. It does indeed. Now @saveasteading knows his way around buildings as do many on BH. I took a step back and looked up at the roof. Up there is a historic roof truss. I can't see enough detail to try and date that without risking embarressment. Now I'm totally guessing here.. but the roof is sitting on old walls that will have moved about, probably spread. I wonder if the railway line is acting as a tie beam (in tension) rather than a vertical load bearing element. Don't forget folk would put in anything to hand in the past to solve a problem. If you look closely the railway beam seems to frame into a beam at the edge of the first floor stiff diaphragm floor. I'm just speculating of course.. but if the railway beam is working as a tie then you could maybe swap that out for a steel rod or stainless steel wire. You need to check you can clear the line of the stair by 2.0m. If you struggle then you could spend a bit more on some fancy catilevered steel connection to raise the height a bit. Don't chuck in the towel just yet if you really want the place.