CLT experience

Kate, We have one under construction, one being bid, and another one in design. The lessons learned so far appear to be: * CLT/DLT/NLT. CLT often refers to the broader term ‘mass timber,’ which includes dowel-laminated, nail-laminated and many other types of subfloor and structural products made from wood and adhesives. * There are going to be joints between CLT panels, occasionally they can be wide and unsightly so see if you can control where they are. Not as important in the field condition as where panels come together in unusual conditions. * FSC or not? In some research the embodied carbon of mass timber from poorly managed forests are on par with steel construction. * EPDs. If you are attempting LEED LCI reduction credits, know that EPDs for timber products can be difficult to find. * Codes. The 2021 ICC codes include 3 new types of mass timber (4A, 4B, and 4C) which allow high-rise construction with mass timber structures. The existing Type 4 has restrictions, and you can also do mass timber under type 5. In WA and perhaps other states the 2021 IBC has been retroactively adopted so you can do those new types. However there are more restrictions so our 5-story mass timber project has seriously considered the old type 4 even though the new ones are available. * Procurement. In WA we have access to several providers of mass timber. There are not yet much consistency within the industry so we often need to pick one manufacturer quite early in the process and work with them to use their preferred system where we are essentially locked in to their detailing and system uniquenesses. * Acoustics. Within an open office space often the dropped ceiling provides acoustic absorption. IN a mass timber deck above you don’t want to cover it so another way to absorb sounds need to be used. * Topping slab. Currently mass timber decking hasn’t been thoroughly tested for lateral loads, so a topping slab is necessary for the projects I’ve looked at. It’s also a good idea from a sound transmission standpoint. Good luck! -Kjell From: Kate

I believe Kjell ( as usual ☺) has captured it all! we have a small CLT one completed (dining/school) and a rather large CLT project (2 story office/640K sf) soon to be complete (and 2 DLT’s in design – one school and one office/hospitality) – so I will add in a little on trends we are seeing/experiencing. Of the 4 we have designed only 1 is all mass timber, the rest are steel and timber combinations (steel beams, wood columns and decks): · Power/Plugs: designing for conduit runs and flexibility. We have ended up added concrete to accommodate floor box depth (☹) though, having to do that resulted in reduction in beam size/weight in certain places. This was a positive consequence but I don’t think was the most efficient or best overall carbon reduction result. o Carving out spacing within the decking while maintaining structural continuity and minimizing amount of concrete requires early (concept/SD) back and forth. · Acoustics: this seems to be hardest item for us right now as we want to see the wood but not experience the foot fall (Impact Coefficient issue). DLT has some sections that allow for insertion of felt or other material to help with acoustics. · According to Structurelam https://www.structurlam.com/ , FSC should only add 5% to the cost…we will see. Go to Structurecraft for DLT https://structurecraft.com/materials/mass-timber/dlt-dowel-laminated-timber · Grids: working with the right grid for the most efficient use of material has been a bit of a challenge if you don’t start there (maybe obvious). Finding the right alignment for program type is key. Gain insight from some structural firms working on this : MKA, Holmes Structures, John A. Martin (relative to fire rating) have great insights – you can find info on their websites . If you want to talk to someone specifically, email me. I will see if we have a Lessons learned deck if anyone wants From: Kjell Anderson

I can’t personally help much, but we’ve been doing a lot of CLT projects and have a resident “expert” here at Hacker. Feel free to contact him directly and say I sent you! Scott Barton-Smith sbartonsmith@hackerarchitects.com Audrey Alverson LEED Green Assoc. Director of Marketing Associate Principal she / her / hers Hacker o 503-227-1254 d 503-972-5363 hackerarchitects.com From: K