Saturday, October 1, 2022

Structural Engineer vs Architect – Design Meeting

a structural engineer is always a part of the design team for every residential project I do then as the outpost project plans and elevations are taking shape it's time to begin thinking about how we design the structure foundation framing and finding a good engineer really does expand what's possible and importantly .

It can begin shaping the design we ought to be thinking about what's the relationship between the the box the building that wants to move like this when the wind blows on it the ledge below is what we need to attach it to and so how do we resolve the wind against the broadside of the barn .

Let our lead down to the ledge do we pour chunks of concrete that aren't going to move in certain areas although you might see those is that a cost-effective way to get the job done as compared to 8 or 10 sets of stainless steel cross bracing for example they they look different they do the same job pouring concrete on an island especially .

A remote island is a big deal there are quality control considerations so we we can't have this we can't use the same pallet of materials on an island let alone a remote island that we can on the mainland so the quality of concrete may be lower if it's site mixed if it's it may be inconsistent while you can develop those strengths in the in a lab .

Easy enough we at times are concerned about the quality of that concrete and if that's what's holding the building up then you want to try to avoid that we probably want to use a series of timber posts that have some typical probably stainless connection to the ledge okay well and and I've done enough work on this island to know that it's not a .

Smooth consistent ledge it's fairly irregular yes and so it may be that if if you want to architectural EC the pecking order of building post maybe stainless connection to ledge ledge might be three feet away yeah if ledge was clean consistent and exposed six inches below grade it would be pasta to install a stainless steel post base .

Grouted level Pindell edge and it may be a custom event plate it's actually cheaper than an off-the-shelf stainless really post base typically so because ledge elevations are fairly inconsistent I'm guessing that we probably aren't going to get away from pouring some amount of concrete into Ledge and that basically will set us up to provide some .

Predictable top of Pierre elevations that will be helpful during the design process and also during our shop drawing review of of any steel components it's good to understand as we're tracking loads down through the building what we're going to have for a dance floor on which to land that so it's good to talk about the site ledge post versus .

Concrete material palate at first and then we actually go up to the top of the building and talk about which areas are vaulted generally what the thickness of roof cavities will be is it a 2 by 12 10 8 etc and there may be varying it may be that low roofs are thinner because of fascias etcetera so now that we talked about site conditions it would be good .

To talk about your ideas relative to typical wall construction is it a 2 by 6 or 8 or 4 in areas and then what are those roof planes what are those roof cavity thicknesses and based on your architectural maybe insulation requirements for example the thickness of that roof cavity it may be that I only need a 2 by 8 in a certain area but .

You say well based on our anticipated insulation detail we need at least a 2 by 10 and that may set up a typical soffit and facia detail around the perimeter of the building also this framing 2 by 6 I think part of the idea here is that almost anybody could build this so I think we have to keep it simple in terms of relationships of roof .

Surfaces what I've tried to do on the elevations is really establish the profile of the building as being quite low so I don't and it we didn't discuss this but this is a 12 foot wide volume here this is 16 feet wide so the intent is to keep everything and small and really so that you are very close and you know connected to .

This environment and so when you start folding that back into the elevations you know the heights of these things are pretty pretty small so we're talking like a seven foot ceiling in here in this entrance and then you know probably a two by ten for the roof framing in here and then I'm planning to frame a flat deck and then use tapered .

Insulation on top of that to get to our scupper at one edge from a framing standpoint we call that flat framing right when the on the framing and the sheathing over the top of it is flat and then you and then you add tapered rigid above that structurally that's the easiest way to do it because you have a consistent wall plane elevation what's .

Your sense are we talking green roof ballast etc or if you were to climb up there would you see the exposed black PPE PDM roof it's very common sometimes you install a finish with some type over yeah ideally we would install something and we had talked about it'd be great if it was a stargazing deck but once you do that it sort starts to level everything .

Up so epdm exposed is what I'm thinking structurally we like that because we don't have to carry the dead load of three or four inches of Riverstone or a green roof for example which at which have their own maintenance issues right yeah so that's good so given that span I think that a 2 by 10 is going to work okay in the sort of pitched roof .

Assemblies and I was thinking the two by twelve a sixteen ish foot span we're in the ballpark for a two by twelve and if it's a 512 then generally speaking we probably have a double top plate we have a two by twelve rafter and two by six stud and then we can talk about the eave whether or not there there is an exposed tail that's a little bit more difficult .

If that rafter was exposed and whether or not that is actually the extent of the rafter whether this is actually ladder framed added to it so that's what I'm picture I'm picturing that I wanted a really minimal overhang but you know we're pretty exposed here so you know just having a drip or something very close to this shingled wall surface .

Probably not the ideal thing so if we do anything it will be an added piece in here and I'm still working as to you know like ideally for me that this surface would be very thin you know and then we would bring this as a metal roof so the the metal roof would sort of come like that and that this would just be almost like a drip edge but if that's .

Six inches you know this this needs to have some some heft to it sure depending on what this is if there is an insulation plane of if it's not the case but if we had an expose to deck here and we had an exposed rafters sometimes we'll embed this thing up in that insulation plane fortunately that's not the case here and so whatever that is .

We'll probably just add it to the side of the rafter okay we refer to it really as an outrigger but it's maybe a two by four for example or if you want it to be even thinner we'll just take a look at what is that cantilever don't be on the outside face of that stud I'm gonna say it's six inches for now no it's nothing if it's only six it may even be applied .

Okay because that in such a case we'd want the roof sheathing to be continuous because that would be our tension tie and if you have a continuous sheet there and you've got a ladder frame thin soffit assembly there then it could simply be applied and we wouldn't necessarily need to break that it's handy to see the building first and then .

Apply that but that's a detail for another day for us okay if you simply were to cantilever the sheathing out there and then apply a finish to the underside of it six inches is not much but at the end of the day you actually need a fascia to be straight and when you have two sheets of roof sheathing even though they're only .

Cantilever in six inches you need to you need to double up a fascia of something of some depth there simply to allow your sheathing to sheathing sheets to not read one thing that we need to consider is when we're choosing our pal materials for this building in a remote environment perhaps assembled by a small crew whatever we use to build it's going .

To get wet and in a night in an ideal world and we do this at times we actually prefab sections of buildings and they actually deliver it in pieces and so the that the floor is framed within a few days the walls are erected within a few days the roof is on within a few days in its watertight ish it's probably probably not going to happen in .

This case and so the more pieces of dimensional lumber we can use for example I was thinking down to the floor and I'm jumping ahead but it would be great to use dimensional lumber as compared to an engineered I joist that doesn't perform as well when it sees some some construction weather so thinking about this detail we just want .

To use parts and pieces that have some durability to them even if they're small quite often here on the coast the structural design is heavily influenced by the lateral loads on a site for example on this site which is really exposed the winds exert horizontal forces that we need to trace all the way back into the foundation and because .

We're using piers for our design this starts to suggest a certain palette of materials and the types of connections we're going to use as we're thinking about connecting this building down to the ledge that's main force let's say and I'm just guessing 20 pounds of square foot applied to that vertical face it's 14 feet tall .

Well that's 280 PLF basically for every length of wall in this direction which is that right there we've got 280 and so so 24 feet so bring out or this beauty six thousand seven hundred and twenty pounds of lateral load that we need to move down to the ledge and so then we say okay this is a short course and lateral this I'm here .

But we have we have this I mean this is how we this is this is what we'll do in our office right every exactly and so in this schematic kickoff meeting we talked generally about the systems and then we start to measure these components figure out what the geometry of the building is what the resulting loads are based on a .

Site-specific snow wind etc and then we figure out okay how much force we actually have in these braces is this wood PT four by eight brace actually going to work which is where we're headed here in a minute right because we said that the weak link of these systems is often the connections so let's say that we have six thousand seven hundred .

And twenty pounds that needs to find its way down to the ledge that's the load that ends up in in the first floor deck right as it's moving in this direction so the first floor deck is sheathed here right and so if this was a really long and skinny building here it may be that you can't to to resist that 660 720 in this direction it may be that you .

Actually need bracing at fairly regular intervals and not just at the two ends because the wind diaphragm just can't bend that far it's a beam it has a width of 3/4 of an inch and it has a depth of 12 feet that's what a diaphragm is right it's a beam that spans but this guy is only spanning 24 feet so thinking ahead it's .

Likely that if if we don't even consider any contribution from this block right here we would only need bracing here and here and we need and we'll have half of that 67 a little bit over 3,000 pounds in each gable end if you will so then the question becomes 67 20 / – were at 3400 pounds or so she thing's going to be nailed to the beam that the loads .

Easily going to be in this beam if we have a wood frame floor and a PT 6×6 post and a PT 6×6 post could it be as simple as not respecting any sort of architectural finish on these posts but let's just think about structure here for a second could we simply take a PT 2 by 10 and nail it to this face and nail another to that face so if we look at .

That condition we're gonna have PT 6×6 post with a maybe a stainless steel bent plate and we're gonna through bolt that's going to be installed on a concrete pier that's pinned to ledge and then we have a floor system up here but what we're really interested in looking at is that connection right there we really want to .

Get this brace as close to the concrete pier where that's headed so we don't induce any additional bending forces in that post because that wants to sort of do that that's right yeah and we're thinking about 3,400 pounds here so let's say you said architectural e that I just want a 2 by 8 there because the 2 by 10 is a pretty significant thing to .

Look at so okay we might have a 2 by 8 there and we have a PT 6 by 6 post that is five and a half inches and we have 3400 pounds in this or maybe there are two of them so let's say it's 1700 pounds one on each face of the post for example yeah if you take a look at the at the wood design guide it tells us what the minimum edge distances are from .

The edge of this brace to the centerline of that bolt and all of a sudden seven and a quarter by five and a half as we lay this out is a tiny little space and and if you look at the capacity of this inch and a half wide member in the other direction let's say you've got a yes a we're looking in that direction let's say you've got one on each side a 16 .

Penny nail is good for 120 pounds something like that okay so 17 nails could we fit that in here probably not and even if you could they'd rust and be gone in a few years so in the other connection there isn't going to work I think we're gonna have difficult time making a bolted connection to work as far as the capacity of that side member .

This is called the side this is called the main member and so if you look in the wood design guide you'll probably see that that five eighths diameter stainless steel bolt with an inch and a half side member is probably going to be good for four hundred five hundred pounds at most and so five hundred a thousand you're going .

To be pretty close point being we're either gonna need a lot of wood braces or a handful of of well-designed and repeatable stainless cross bracing and so if this thing was a stainless brace it's likely that we could have a through bolt and then make a connection between a stainless brace and a tie here for example and start to .

Develop some of those the key is to make the connection to the to the wood post or if we can standardize these guys it may be that we have a connection and it takes it right to the concrete through that off-the-shelf post base I'm just worried that we're not going to be able to find any kind of consistency as I look at the site plan it's all over the .

Place and and so and especially even given how things change from front to back on that unit I just I don't want a big concrete piece that we're gonna have to look at that because I'm not sure I trust the level of finish that's gonna happen with some of those concrete pieces so I to me you know it's preferable here does that does this .

Connection get a clevis like does it come to that kind of a thing or a pin or how does that yeah it likely would be a through bolt or a bracket of some type that has perhaps an eye and then a clevis okay so it so the clevis is like that's right here's our I that's right right this gets tagged into the post and .

Then you said that's a through bolt connection County it's likely a through bolt depending on depending on the angles it may be that that's a bracket of some type that's bolted that's jacketed around the post for example I think in an ideal world it would be a bolt for example and I bolt if the forces are low enough then we can .

Actually develop that connection okay I'm fine with that as a look as we continue our discussion we reviewed the first floor framing package and the exterior deck construction details and finally the barn and I wanted al to address one of the most common objections I hear in the field during construction it's always necessary .

People have built buildings out on this island for you know a couple hundred years right this is a question I get all the time from builders saying you know I can do the back a napkin calculation that's that's a 2 by 10 for that floor and it's 2×6 wall I'll throw a few nails in it and call it good why why do we go through all this trouble with these .

Homes with architecture in general sure well I think it comes down there are a few variables one is how aggressive is or based on the architectural requirements of the building how aggressive how hard is the structure working and so if you look at this simple little box right here the structures not working very hard I think .

It's going to work a little harder over here a general contractor could easily assemble these details and it would for this little box and it would perform quite well as a consultant I work for you the architect and it's your responsibility I'm not trying to tell you how to do your job but generally speaking you are having a variety of .

Conversations with the owner and those are pretty deep conversations and you are understanding their performance expectations for the building it may be that the owners say we want to use fairly inexpensive windows for example we're going to use wood finishes we just want a clubhouse and we don't want water to come through the roof that's a far .

Cry from $100,000 slide door where the allowable deflection below that sill is zero and so that's where those things come into play right when we start doing well before that big openings that's right but that's the white in the yellow line yeah for us as structural engineers so so that sort of describes the spectrums .

You're in which we work and so my dad was a builder growing up and I saw him build all sorts of things that structurally don't quote unquote work on paper but they actually worked for him and his clients because they met the performance expectations that they had for the building and so I think that there's there's a basic level of .

Performance that if I put myself in a homeowners shoes I'm investing enough to and I care enough about the product that I'm gonna hire an architect and I actually care that that light switch is however many inches off the floor that you put it when you walk through the door I don't know what it is but yeah but you do right yes and so when they .

Walk into that building they may not know that or they may not always be directly aware of the benefits associated with hiring a professional but they know that when they go into the bathroom that it works well because they were able to reach around the corner and turn the light on right when we don't do our jobs yes of .

Course a building could fall down which which doesn't happen except in a very rare occasion on a different scale but it's more that there's a crack in the sheet rock or the plaster or a window leaks and people think that it could be a product failure and it may be but it's probably a combination of things and it may be that .

That window wasn't properly flashed it may be that the building actually is moving just a little bit too much and so if you look at the average 24 36 a home in a subdivision the performance expectations are probably low they've been built a million times it's a commodity people know how those go together and so do you need a structural .

Engineer to design those no you you don't at all or in a very rare case but once there's something unique about the design I think it's that's when professionals get rolled in to make sure that it performs as well as we as a professional think it should if that makes sense based on our conversations with the .

Owner and that ultimately the owners are happy and if you've got a building if you've got windows that leak for example that's not that's not performing particularly well yeah and I think there's also I mean we haven't talked about it much here but there is also you know architecture interfaces with structure and I think the best .

Architecture it exposes that structure for how it performs it turns into something beautiful and I think that you know that collaboration for me is if I have an aesthetic goal and you're able to help me get there like that's it's an interesting conversation to talk about you know well if the goal is to pull the the columns in here .

You know there's lots of different ways of doing that here's the implications for me that's an interesting dialogue to have and then you know this doesn't have a lot of exposed structure in it but like for example if I was gonna do that in here you know this is the this is the space I'd want to do it putting those items on the table so that we can .

Discuss them and really hash out what the what not only what the structural implications are but also from a cost standpoint I mean because all these things are interrelated that's the thing about architectural design is it's not just one thing it's we have the Builder that we're interfacing with we have the structural goals we have the .

Architectural goals function aesthetics you know all these things kind of come together in this space and I think that's you sort of answered the question exactly how I hoped you would in that yeah do we need an engineer to make sure that this thing doesn't fall down you know maybe not but does it make it a better product does it make it .

Architecture involving one I think it does to have you as an expert that contributes to the process in a meaningful way that actually shapes the design that's where it's really important to me you know I think there's there's something interesting about as a consultant so generally speaking we're 10 ish percent of an architect's fee if .

You if you actually look at the business plan which means we actually need to cycle through ten times the number of jobs that you do if we were to make it be the equivalent living which we do and so we on some projects lightly touch we may size a couple of beams we may provide a full set of contract documents and construction .

Administration services for four other jobs but we're the guys who are helping to put together the drawings that describe the bones the building and how it connects to the to the ground obviously but we're also involved in ten times the number of jobs and we see stuff that doesn't work and so if we occasionally offer architecture quietly .

Out of the side of her mouth for architectural advice it's because we're exposed to so many projects and so it's not just the the calculations to make sure the Dean doesn't deflect it's sort of a global view about the construction industry practices what works and what doesn't work and oftentimes is what doesn't work and I .

Don't see anything here that doesn't work but that's often our value to know these early meetings don't suggest the final solution but knowing the structural forces that govern a project allow us to account for them and resolve them in a meaningful and hopefully elegant way oh look at that baby that is what year is that there might be .

The same one I have the 9th edition yes let me see I'm gonna have the ninth edition – look at that the difference between an architect and a mansion here who's doing more work here you


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