Seeking advice on house plans

[Ian_Driscoll92]

I'm in the middle of drawing up the plans for my house I'll be building next year. 22x32 two story timber framed house.  White pine for the frame, oak braces.  12/12 roof. Galvanized steel roofing.  Most likely going to do a modified Larsen truss with blown in cellulose, 8" for walls 10" on roof. 68 psf snow load for my area. These plans are not completely done and have been hand drawn, so if it seems like there is anything missing, it's because I'm at a point where I could use some advice.  I've built timber frames before but am self taught and I have always built on a smaller scale, usually just copying what I've seen in old buildings.  So the design process is foreign to me and I lack confidence calculating loads and timber sizes.  I feel like the timbers are oversized in my plan and ideally would like to downsize wherever possible. Any advice or criticism is welcome.




 

 



 

[Jim_Rogers]

Personally, I don't like drop in dovetail purlins in a roof system. That's because of the shrinkage situation.
You can't rely on them staying in the rafter.


 

In the above picture the dovetail shrinks along the red dimension. And others used to pound in wedges at the blue line to hopefully hold the dovetail in. As I have never done it I don't know how it works.

Jim Rogers

[sawguy21]

Welcome aboard! I am not familiar with timber framing but am not a fan of galvanized roofs. My parents vacation cabin had one as it was easy and cheap to install but during rainstorms we couldn't hear ourselves think. Don't put entry ways under the eaves especially if you get a lot of snow.

[Ian_Driscoll92]

Thanks for the quick reply Jim.  What is a method you would recommend for the purlins?  Any thoughts of if I got the sizes of the Timbers right and if using small dimensions are possible?

[Don P]

If you look up in the roof at the 2 posts, if you can carry those down through the structure it becomes easier to downsize the timbers.

On any of these drop ins, the floor is potentially the same way, the width remaining between pockets is the design timber dimension. that 7x10 can quicky become a 2x10 trying to support several floor joists. If you can either stack the joists and purlins on top of the beams, tenon them into the center, neutral axis of the girder. Or use concealed hardware. Then you can reduce timber sizes, or rather use more of the timber as design dimension, "net section". 

[Brad_bb]

I would (have) started with a floor plan for each floor.  Laying how all your spaces and figuring out home much room you need.  You need appliance dimensions, if you can use actual furniture dimensions and lay it out in the space, Bathrooms need very specific layouts depending on the tub/shower vanity/sink, linen storage, cleaning supply and TP storage.  Layout your furnace, water heater.  How much room is needed for the fireplace or wood stove... Figure out where heating trunks, plumbing and electrical will come up from below.  

You'd hate to build it and realize if I only made it a foot wider here or there...

Yeah, I start with the floorplan layout with as much specifics as possible.  Figure out the frame design after.

[thecfarm]

I always say put 3 foot door everywhere, inside and out. Even in the bathroom.
We did on the house we live in. Wife was in a wheelchair many times. The 3 foot doors made it very easy to get around.
Also helps in moving furniture in.
When they came to move the funiture in from where we brought it, I heard one guy tell the other, this will be easy.   ;)

[Jim_Rogers]

What is a method you would recommend for the purlins?  

One thing to consider is how to hold the principal rafters while you place purlins in between. It requires lots of straps and come-a-longs:


 
You can see in the above picture that he had to use many straps and come-a-longs to hold the standing bent so that he could lean it out to place the purlins in between the principal rafters.
The crane flew the purlins in. To make sure that these purlins with tusk tenons on them didn't slide off the marks he put cleats on top of the rafters. Like this:


 
Then each purlin had a cleat attached to it that stuck out beyond the tenon so that when the crane lowered one down it would catch on the rafter cleats and sit there until the come-a-long was tightened up and pulled the bents together.


 
Sorry I don't have a photo of the purlin with a top cleat on it, that I can find.
To make a frame go together a lot easier, I prefer to use common rafters. Raised in pairs with a temporary collar board between them. No ridge beam needed:


 
Once the rafters are seated, secured, plumb and then braced off, you can remove the temporary collar board.
To me, much easier, and no need to purchase hundreds of dollars worth of straps and come-a-longs.
And as DonP has mentioned the principal rafter is not reduced to a smaller size by opposing notched for purlins.
Many frames are done with common rafters. When sized correctly for the load, and evenly spaced out that make a solid roof system. 
But these are just my thoughts, and opinions.
Jim Rogers

[Chilterns]

Hi Jim,

Your thoughts and opinions are well placed !

What are the bits of wood attached to the principal rafters ?

Please explain the term - "cleats"

C.

[doc henderson]

a cleat is a chunk of wood or other material placed temporarily to help with assembly in this case.  so, the purlins cannot take off down the rafter.

[Jim_Rogers]

a cleat is a chunk of wood or other material placed temporarily to help with assembly in this case.  so, the purlins cannot take off down the rafter.

Yes, as Doc said. shown here with arrow:


 
You'll see many of these in the other photos I posted.
They were most likely 2x4s about 16" long or so.
Jim Rogers