Building and Construction - Roof Structure. Raised Ceiling Joist

Author

Roof Structure. Raised Ceiling Joist

skibs@skynet.ie

2006-03-29, 11:21 am

Hi Everyone,

I am re-roofing my home in Ireland. I'm a DIYer, not a pro!

My span is 20ft, Wall plates are anchor bolted at 48" centres.

The pitch is a weird 36 deg (Had to run to meet the chimeny flashing!!)

I worked out the rafter length (148" 5/16

) and put up 4 master
rafters(2" x 6" C18 grade) along with ridge board.

All goin well so far!

I am putting in a purlin flush with rafter at rafter mid point.

The problem is I want to raise my ceiling joist about 18" up offf the
wall plate.

Should I collar tie 18" down from ridge?

Should I still use a hanger from purlin to joist?

What about strut from purlin to celing joist? Do I need to have a
supported runner to carry the struts along the ridge line at celing
joist level?

The next part of my roof hips into this roof, its span is 15 1/2 ft. My
plan is to valley rafter to the 20 span roof ridge and use a shortened
valley rafter on the other side.

>From the rafter tables, it looks like I'll just about get away without
using a purlin on this one. rafters are 2" x 6" C24, good'n strong ;)

Again here I presume collar tie below the ridge?

And the same raised ceiling joist happens here also! Will I need to
strut for this?
Will 4 10d nails do, or should I bolt or use some special ties?

any info appreicated.

Kind Regards
Pat!

DanG

2006-03-29, 7:21 pm

I really hate it when other responders jump up and tell a poster
to go consult a structural engineer while making no attempt to
help the OP.

Some of our terms may be different, but I think I followed your
description. You have a system of 2x6 rafters from ridge to top
plate. Your ceiling joists do not meet or fasten to your top
plates. Your are hoping that side nailing the ceiling joists to
the rafters at a position 18" above the top plates that you will
be able to control the horizontal side pressure pushing out on the
walls.

You are planning on adding stiff backs to both ceiling joists and
rafters and tying them to each other.

If I have diagnosed where you are going, it actually sounds fairly
good. My concerns would be the horizontal pressure on the outside
walls and the deflection of the ceiling joists because of the
rafter purlin load. I hate to bale out on you, but I think I
would sketch it enough to go talk to structural guy. I have seen
2 expensive homes literally push themselves apart due to lack of
sufficient engineering to control the outward thrust of the
rafters.
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)
dgriff237@7cox.net

<skibs@skynet.ie> wrote in message
news:1143644235.694034.140030@v46g2000cwv.googlegroups.com...
> Hi Everyone,
>
> I am re-roofing my home in Ireland. I'm a DIYer, not a pro!
>
> My span is 20ft, Wall plates are anchor bolted at 48" centres.
>
> The pitch is a weird 36 deg (Had to run to meet the chimeny
> flashing!!)
>
> I worked out the rafter length (148" 5/16

) and put up 4
> master
> rafters(2" x 6" C18 grade) along with ridge board.
>
> All goin well so far!
>
> I am putting in a purlin flush with rafter at rafter mid point.
>
> The problem is I want to raise my ceiling joist about 18" up
> offf the
> wall plate.
>
> Should I collar tie 18" down from ridge?
>
> Should I still use a hanger from purlin to joist?
>
> What about strut from purlin to celing joist? Do I need to have
> a
> supported runner to carry the struts along the ridge line at
> celing
> joist level?
>
>
> The next part of my roof hips into this roof, its span is 15 1/2
> ft. My
> plan is to valley rafter to the 20 span roof ridge and use a
> shortened
> valley rafter on the other side.
>
> using a purlin on this one. rafters are 2" x 6" C24, good'n
> strong ;)
>
> Again here I presume collar tie below the ridge?
>
> And the same raised ceiling joist happens here also! Will I need
> to
> strut for this?
> Will 4 10d nails do, or should I bolt or use some special ties?
>
> any info appreicated.
>
> Kind Regards
> Pat!
>

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