Tie down, Top plate mortises, insulation, raising questions

This topic contains 3 replies, has 3 voices, and was last updated by roger michon roger michon 2 months, 1 week ago.

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  • #17984
    roger michon
    roger michon
    Participant

    HI Brice

    I have a few questions, your feedback will be greatly appreciated.

    I thought I would start with a little background. My cabin is being build a few thousand miles from home so time is limited by the distance as well as having to stop working in early September to get back to work. The location is about a mile of road then 300ft through the bush. We can’t bring in a crane but  if the weather cooperates a tractor will be used to raise the 4 bents. The second floor and roof will have to be done manually. The cabin will be protected from wind on the East, West and south sides. A north eastern wind can happen without notice and needs to be considered, as explained below. The sills, 4 bents, girts, etc are completed and standing, see pictures on your raising page. The top plate is ready with the exception of the 4 post mortises. All roof rafters are cut, just have to do a few test fits.

    Cabin specs:  outside   36’L x 18’ W x 20’11” H, 2 – 8’ decks,  under the  roof line, inside 18’ x 28’, loft 18’ x 12’,  roof pitch 12 x12, Posts/girts/cross tie are 8”x8” and  8” x 10”, Sill plate and cross sills 8” x 10”,  Rafter  5”  ½  x  7”  ½  x 20’ w step lap rafter seat ( 5’1” overhang)   Top plates   8”x 10”x 37’3”, loft floor Joyce 4” x 10” x 18’. All beams were cut from western spruce..

    Wind/screw jacks/tie downs

    1)      We have 8 levelling screws jacks which will be placed below each post, the wind from the North can easily blow 50, 60+miles an hour.  The upper and lower decks have a 10 roof overhang which of course faces north. I am concerned the wind will move the cabin off of the jacks over time. Some people think I am crazy and say it will never move.  I  am considering lag bolting the jacks into  the sill plate then drilling 6 ft into the clay base and installing 4 anchors to attached to the sill plate or putting the cabin on the crushed stone pad with 8 – 4’x4’  cement pads but that will make it difficult to level if/when it settles, any suggestions?

    Raising:

    Top plate

    2)      Did I mention the front of the cabin will be about 12ft from a 30 ft drop to a creek, east and west sides have trees ( major wind breaks)  5 to 10 ft from the sides so access is limited to the back of the cabin. The timbers were cut over 3 years ago, they have a few  twists so the tenons for the top plate are not straight.  I decided to raise the frame then cut the top plate mortises.   As you know the 8” x 10”x 37’ top plates are very heavy and I would like to limit the amount of times I hoist them up. Once the frame is up my plan is to measure from tenon to tenon with a laser measurement tool then again from reference side of each post to plan the mortises. What would you do? Should I oversize the mortises a little?

    Rafters

    3)      Moving on to raising the rafters. I’m thinking the tractor will have to lift them onto the south end of the top plate then we manually pull them to the north end to raise. I’ll have a heavy duty piping frame drilled in at the front so we can tie on and pull up the rafters…  I’m open for ideas or any video’s you know of for this type of raising.

    The rafters have a step lap rafter seat to lock into the top plate so that should make it easier and safer with cross bracing of course.

    I’ll thinking of securing the rafters to the top plate with threaded rod ,  washers and nuts. Is there a better way? Don’t really want to see the nuts and rods but would like to keep the roof in place on a windy day. What the best way to drill straight through the rafters and top plate without buying an expensive gig?

     

    Roof and floor insulation

    4)      For the roof I’m thinking of sheeting with plywood,vapour barrier,insulation then the tin roof. Is roofing ice shield considered a vapour barrier? What type of vapour barrier is best to use?

    Have you heard of anyone insulating above the subfloor to avoid mice issues in a cabin? I like a warm floor but couldn’t put in more than 2” foam for height reasons above the subfloor.  Would there be a potential vapour barrier issue between the subfloor and the finished floor?  If that’s not the way to go the sills are 8” x 10”. I’ll put 8” of insulation in the floor and treated ply on the bottom, I hear mice don’t like treated wood.

    5)      I’ll be making the hurricane braces to tie the posts to the sills,  was thinking 16” x 6” of 3/8 or ½ steel plate, what do you use? Thanks so much

    Roger

    #18048
    Richard Guggemos
    Richard Guggemos
    Participant

    Hi Roger,

     

    I know that your questions were addressed directly to Roger, but ATMO at least some of them might be better addressed to a structural engineer specializing in timber frame.

    This isn’t intending to be mean, and I’m no expert, but somethings about your post suggest may have put the cart before the horse.  Moreover, it warrants consideration that Bryce is offering his assistance and this forum for free.

    There aware also some factors in your description that might warrant clarification, to wit:

    – what is the distance between center of the principal bents?  Is one supporting a projecting roof?  And if so, how does your plate length relate to the length of your cabin?

    – are you providing any support to the tie beams along their 18’ span?

    – how are you supporting the 5-1/2’ overhang of the roof eves?

    – are you employing king/queen posts or some form of truss to support your rafters?

    – why are you employing screw jacks under the posts and how do you propose to engage them with the posts and or sill beams?

    – are you building directly on clay?  Or some kind of foundation.  If so what?

    – where is the upper deck? Where does it’s 10’ roof overhang come from (numbers don’t add up as I see it)?

    – given your wind zone, do you really want a big upper deck that the wind can get under?  Same for 10’ over hanging roof and 5-1/2’ over hanging eves.

    – how would concrete pads on crushed stone prevent the (very heavy) cabin from moving?  Especially compared to anchors sunk into the ground?

    – can you clarify location and cabin faces?  You’ve used a combination of compass points and “front” and “back” that cause the reader to have to make assumptions.

    – have you studied any of the books on raising timber frames and some of the devices (often primitive) by which to lift heavy bits and bobs?  It might help you immensely to do so.

    – have you looked around this site to examine the various hardware Bryce  sells for securing connections in youth timber frame?

    – how stable is the 12’ of ground between the cabin and the 30’ fall into the creek?

    – how twisted are the posts?  How much more of the top plate’s overall width will be cut for mortises to accommodate the twisted tenons?

    – and so forth.

    Hope this doesn’t sound too snarky.  Just trying to clarify your questions and maybe redirect some of them to better placed resources.

     

    All the best on your endeavor,

    Ricj

    #18062
    Brice Cochran
    Brice Cochran
    Keymaster

    Sorry for my delay, I have been traveling a bunch over the past couple of weeks.  Here are my answers and thoughts…

    1.  Call an engineer you can find one at https://timberframehq.com/timber-frame-engineering/, I like to sleep at night during a storm.

    2. Since you are going to have to take the frame apart before the install can you measure everything, cut the plates and pre-assemble it in the shop on the floor or on sawhorses to make sure it fits before heading out to the site?

    3. If I am seeing it right in my mind you could just use some good structural screws.  I would also recommend consulting an engineer for this connection.

    4. Where is your project again?  There are a lot of building science articles out there for timber frames but system vary due to location.

    5.  That sounds reasonable, I have seen a lot of engineers spec out heavy duty Simpson straps for that connection as well.  See our detail at https://timberframehq.com/sill-plate-to-post-joinery/.  I would also recommend consulting an engineer for this connection.

     

     

     

    #18073
    roger michon
    roger michon
    Participant

    Thanks for your reply’s I’ll look into your suggestions. The posts are twisted  about 3/8″ to 1/4, as mentioned , I would like them to fit the first time. There no room in the shop to pre fit them,  I was thinking over sizing the mortise a touch wouldn’t be a issue on the  8″x 10″  top plate.   The entire cabin will be on stable ground, hard clay with 6 inches of packed gravel. The front of the cabin faces north, the back, south, it’s completely protected from the wind on east, west and south sides. The screw jacks were for levelling however they are no longer going to be used. The cabin will sit on pad and will be secured from any movement.  To clarify the upper deck is on the north end as well as the lower deck. The upper deck is accessed from the loft, the lower deck from the kitchen area both are under the roof line. The top plate is 36 feet long, the roof extends 2 feet over the the ends of the cabin so a 40 foot roof. The decks are 8′ with the 2′ roof overhang is where the 10′ I referred to comes from, that may of been the wrong term to use.  The interior  of the cabin is 18′ x 28″.     The designed was engineer approved which included all beam sizes, roof  trusses, snow loads etc for the area. The frame has been built to spec and is only off by 1/8 of an inch on the north end which is due to the small check in the bottom plate. With the limited space at location the raising of the roof beams are going to be a interesting challenge but I continue to discuss options with professionals. This being my first timber frame I maybe a little over cautious but that’s ok. I’ll certainly look into different hardware to secure the roof to the top plate. I hope this clears up some of your questions,  I really appreciate your comments and feedback

     

     

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