[dsec123]

hi! i live in a 1 1/2 storey house. the second floor ceiling is attached to the underside of the collar ties that hold the roof rafters together.

i was thinking about increasing the ceiling height and opening the space up so that the drywall meets underneath the ridge, kind of like a little cathedral ceiling. this would expose the collar ties, which are currently dirty old 2x4s (house was built in 1946).

if i wanted to replace the collar ties with cable or steel rods or something that looks nicer, it seems to me the sensible thing to do would be to install the rod (or cable) directly under the 2x4, tension it until the original collar tie is no longer doing it's job, and then remove the 2x4.

is there a tool or a gauge or something that measures tensile strength in a wood member? something i could clip on to the 2x4 that would show me tensile strength, and slowly go down to 0 as i tensioned the rod/cable?

or is this an asinine way of going about this altogether?

 

[Daniel Holzman]

I am not sure you fully understand the function of collar ties. The ceiling joists are intended to carry the outward thrust on the walls generated by the ceiling rafters. If you were able to measure the stress in the ceiling joists (which requires special equipment not commonly available), you would find that the ceiling joists (also known as rafter ties) are in tension, because the walls are forced outward by the rafters, and the ceiling joists pick up the load.

The collar ties are intended to equalize uplift pressure on the roof during high wind events. If the collar ties were installed after roof and rafter installation, the collar ties would carry no load under normal conditions, since the outward wall thrust would be carried entirely by the ceiling joists. Under normal load conditions, you could remove the collar ties and there would be no change to the configuration of your framing.

During high wind events that generate uneven loading on the roof, particularly uneven uplift, the collar ties distribute the load across the roof, and are useful in minimizing the potential for roof failure. Under certain conditions, the collar ties can go into compression, so use of cables is not recommended, since cables obviously cannot carry compression.

If you want to get rid of the ceiling joists and collar ties completely, two common methods are to either replace the ridge board with a structurally designed ridge beam (expensive, complex operation), or replace the rafters and ceiling joists with roof trusses (expensive). There are a few jurisdictions that do not require collar ties at all, check with your local building inspector to see what the rules are in your area.

If you are required to have collar ties, you may want to consider replacing them with attractive lumber, or just paint them and call it good. I do not recommend replacing with cables. You could use steel rods, but you need to make sure they are designed to handle compressive loads during high wind events, so the rods do not buckle.

 

[dsec123]

hi! thank you for your reply. i believe i was using the wrong terminology and confusing "collar tie" for "rafter tie". i thought they were automatically called collar ties because they are in the upper third of the roof.

anyway with that misunderstanding out of the way, if i wanted to replace the rafter ties with rods or cables, what's the simplest way of doing this?

attached is a simple picture showing existing conditions.

 

[Gary in WA]

Your collar ties are also serving as ceiling joists for the drywall. The problems come when adding the required thickness of insulation and rafters sized to carry today's code requirements for ventilation above the insulation. Or you could add foamboard to the face before replacing drywall; http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/adv_weather_packages.pdf Check with local AHJ.

Gary

 

[roobinsteen]

Gary-the collar ties in this case are not supporting any drywall now, if I understand the original post. Nor will they ever be, it's just that with they will be exposed if the OP decides to drywall up the rafters, and the OP thinks the collar ties look crappy, thus asking if they can be replaced with something else. Here's my suggestion: They probably could be, but it would be a pain, and more trouble than you think. Just make peace with the old collar ties. Sand them if you want, or paint them or do whatever you want to pretty them up.

 

[Gary in WA]

Yes, tired will do funny things.... check with local AHJ as said earlier; http://www.finehomebuilding.com/2001/03/01/removing-collar-ties

Properly sized rafters; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_par027.htm?bu2=undefined

ventilation; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_sec006.htm?bu2=undefined

rafter insulation; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp

Gary- and still tired...

 

[dsec123]

hi, thanks for all the replies!

so just to be clear, are these things called collar ties or rafter ties when it's a 1 1/2 storey?

 

[Daniel Holzman]

To be clear. A rafter tie is a horizontal structural element intended to resist outward thrust on the walls. A rafter tie is normally located at floor level, and is usually the same as the floor joist. A collar tie is a horizontal structural element usually located approximately 2/3 of the way from the floor to the peak of the roof. A collar tie IS NOT A RAFTER TIE. The collar tie is typically too light, and in the wrong location, to resist outward thrust on the walls generated by the rafters. For pictures and further discussion, see https://www.nachi.org/collar-rafter-ties.htm?loadbetadesign=0

You CANNOT REMOVE the rafter ties unless you undertake expensive work to replace the ridge board with a ridge beam, properly size the rafters (probably need to be larger than the existing, and connect the rafters to the ridge beam using appropriate brackets. Alternatively, you can install roof trusses, which do not exert any outward load on the walls, and do not require rafter ties, since the truss replaces the rafter.

 

[dsec123]

ok. so in my case they are probably collar ties, as i originally suspected. the rafter ties would double as the ceiling joists for the first floor. the collar tie doubles as the ceiling joist for the second floor, and frankly that might be it's only function. it may be resisting uplift pressure but i don't really know how to tell that.

 

[Daniel Holzman]

Collar ties always work to resist uplift pressure under high wind events, as long as they connect both sides of the rafters together. That is what they do, the only thing you need to do is verify that the collar ties are in the correct location (approximately 2/3 of the way up from the ceiling level to the ridge board level), they are adequately sized (minimum 1x4), there are enough of them (minimum every third rafter), and they are properly connected to the rafters (typically three minimum 10d nails each side). Collar ties are not specifically intended to be used to support drywall, but apparently they are used for that purpose in your house.