Ask The Wizard

This category of our Blog is filled with questions submitted by you, our customer, and answered by our in house expert, aka "The Wizard". Feel free to browse through to see if your question has already been asked, and answered. If it hasn't, you can submit your question for our expert on the "Ask The Wizard Page" under the Blog tab at the top of the page.

The plates have loosened or fallen off the bottom joints of some trusses. How can I repair that?

Q: I am with Re/Max in Qualicum Beach, but for many years I built homes on the Island. Today I was informed by a home inspector of a problem with trusses and on review all the joiners along the whole back centre section of a roof had failed. The metal clamps had either loosened off or in some cases fallen right off the truss leaving the roof very soft. We are looking for a solution to repair these joints that will pass future inspections, do you have any advice?

A: Wow!  That’s not good.  In order for the trusses to perform as intended, all the connector plates need to be in place! The connector plates must be factory installed and cannot be added or modified on site. The trusses will need to undergo a review by a structural engineer and could possibly be made good again by applying plywood gussets sized correctly for the forces in the joints. The engineer will be able to provide that information and seal for approval to pass future inspections.

Do you prefab custom stairs?

Q: I need a set of winder stairs to go from our main floor to second story. There will be one or two stairs, then a right hand turn, 7 stairs and then another right hand turn. I have it worked out to 16 rises. the horizontal distance maximum is 140 inches, the total rise is 115 inches to the top of floor. Can this be shop built?

A: Your question about your stairs can be answered with a YES!  We can shop build a set of stairs to meet your exact requirements. We just need confirmation of site conditions and dimensions prior to fabrication.


Need a quote for your set of custom prefabricated stairs? Contact us now!


What is the cost difference between trusses for asphalt shingles and trusses for concrete tiles?

Q: I am working on a research project at BCIT and was hoping you could provide me a ball park costing number for roofs going from asphalt shingles to concrete tiles. Costs increases in both the material and time to design per square foot or meter would be ideal.

A: This is a great question that I bet a lot of people would like to see an answer to. Because of the difference in weight of the various roofing materials, there is definitely a difference in truss cost as well.

There are a couple of factors that increase the cost of the trusses and the first one is mainly the additional dead load. With the extra loading the distance between webs (panels) must be decreased and the size of the connector plates increases too. Lumber species and grades all go up too. These all add to the cost. Another item to consider is long term deflection of the panels in the truss. Though a 2×4 top chord is capable of supporting the additional dead load imposed by the concrete tiles, the effect of this heavy roofing material can tend to bow the top chords down between web joints over time – long term deflection. A solution is to shorten up the panel lengths or perhaps go to a 2×6 top chord. Both methods have an effect on cost and design time.

Depending on the clear span of the trusses, the snow load, the roof slope and the truss configuration, the additional weight may have little effect or it may significantly increase the truss price.

So, with all that said and assuming that you are talking about concrete tiles – which may add as much as 15 pounds per square foot to the roof – I would say from past experience that on an average, a concrete tile roof could cost as much as 15% more than a conventional shingle roof.

I hope this answers your question but should you require more information or answers to other questions, please feel free to contact me.

Is there a truss I can install that later could be altered to become the floor of the next storey?

Q: I have a cabin in Invermere, BC that has a shed roof that I intend on removing, replacing the rake walls with regular walls and then replacing the roof with new trusses, etc. Someday I might want to add another storey to the cabin, so my question is: is there a truss I can install that later could be altered to become the floor of the next storey? Perhaps a combination of I-beams and trusses?

A: This is a very good question and before I answer it there are some points to consider. First, I see you’re building in Invermere so ground snow load will be a concern. Second, the span of the truss may limit you to what you can do.

Roof trusses perform just great when they’re used as roof trusses but when floor loads are added, suddenly things become a bit more difficult. It sounds to me like you would want to build a flat truss for now that will act as a roof truss and when budget permits, this will become the floor truss for the next storey. This will work and a roof/floor truss design could be used but I’m not convinced that it’s the most cost effective way to complete your project. You will have a set of trusses that will be the roof of your cabin for now then you will have to get another set to form the roof when you raise the walls.  With that said let’s just assume that this is the way you want to proceed.

The depth of clear span floor trusses is governed primarily by the load they support and the distance between supports. If your span is not too long then you can probably be happy with a floor truss that is designed to carry both the intended floor load and additional capacity to handle any snow that will accumulate. Again, depending on the clear span you could be looking at depths from 16” to 24”. You would have to give some consideration to the type of roofing material that would be used so that it can easily removed after when you go to start phase two.

So, building a set of clear span floor trusses with roof loads on them is really no big deal. The span will determine the depth and you can use 1 inch of depth per 1 foot of span as a guideline.

If you need a more definite answer, please forward a sketch of your proposed cabin with dimensions and I would be happy to give you some more advice and possibly a solution.

After the wall panels are installed, does the 1 1/2″ void get filled up?

Q: With the wall panels, after they are installed with the 2×4 horizontal strapping, does the remaining 1 1/2″ void get filled up with more Styrofoam? Also how big, long and wide, do you make the wall panels?

A: Yes! Our wall panels do contain a 1-1/2” void that we commonly supply 1” EPS (extruded polystyrene) rigid panels for. The reason for the 1” panel is to leave a 1/2” void that you can run your electrical wiring through.  Once the wiring is installed and complete, the infill panel is then set in place and drywall installed over.

As far as maximum dimensions for our wall panels goes, we are only limited by a few factors. Probably the most influential factor is shipping width. We must keep the height of the walls to something that can still be shipped down a highway, or even less when shipped in a container bound for remote areas. Typically walls are constructed at either 8’ or 9’ and are broken into panel lengths to suit the plan requirements. We can build panels up 20’ long if required. We even make tall wall panels for vaulted ceilings by splitting them and shipping them sideways.

I hope this answers your question about our Pacific SmartWall® panels but if you need more information please feel free to contact any one of our knowledgeable sales staff.

2x6 Pacific SmartWall® Diagram 10.09.2014-640x480

Do you recommend nailing trusses to the top plate of interior walls?

Q: Do you recommend nailing trusses to the top plate of interior walls or do you recommend 2×6 nailed to the top plate between the trusses? How would you secure the interior walls so they do not bow if they do not have another interior wall at 90 degrees to it?

A: Thank you for asking such an important question regarding attachment of roof trusses to interior walls. This is a topic that comes up time and time again and there are several ways to answer this.

Remember – trusses are made of organic material (wood) and because of this they will always be influenced by their environment. Because of the nice warm bottom chord nestled comfortably in the ceiling insulation and the top chord exposed to the cooler moist air in the attic space, the trusses will be under different conditions from top to bottom. These different conditions of moisture and temperature tend to cause the wood within the truss to move, shrink, bend or a combination of all. When this happens we have a condition called “Truss Uplift”. This term can make any contractor or truss company cringe.

The fact is… truss uplift is a very real condition and it will happen in areas where the temperature varies greatly from season to season. Truss uplift is with us for good but it’s how we deal with it that can make or break a good truss installation.

Back to your question about nailing a truss to the top plate of an interior wall. I would not recommend this because of what I have seen in the field and depending on how much truss uplift occurs, there can be quite a bit of separation at the drywall edges. I’ve gotten calls where the customer is upset that their drywall that was installed beautifully last summer is now cracking and there are all kinds of gaps in their ceiling at the interior walls.  I am often asked if maybe the trusses have been built too light or the girders are not strong enough and my response is, it’s difficult to explain the effect of truss uplift but this easily avoided problem occurs more often than you think.

So, truss uplift is just part of life.  How do we deal with it? Let the trusses do what they will do and find a better way to let it happen that will not cause any problems. If done correctly, trusses can move as they will, the drywall can move and bend with them and the homeowner never sees the effect.

There are a couple of ways to make this system happen. Simpson Strong Tie makes a truss clip that is basically an “L” bracket that has round holes that allow nailing to the interior wall and slotted holes that a nail is driven in most of the way. When the trusses lift up, the nails can slide in the slots while still keeping the walls plumb and in place. Drywall clips are required at the top of the wall to keep the drywall firmly attached to them.  If the nearest attachment point of drywall to the underside of the trusses is at least 16″ then the drywall will actually bend slightly as the trusses move and return to normal when the trusses settle again. No gaps!

Another option is to nail blocking to the top of the interior walls to secure the drywall to and again, start the first fastener for drywall at least 16″ from the interior wall.  This will work equally well for trusses that are parallel or perpendicular to the interior walls.

I hope this answers your question. Thanks!

Click on the link below to view more detailed information and diagrams.

Icon of Partition Separation Prevention And Solutions Partition Separation Prevention And Solutions (569.6 KiB)

Putting a new roof on an older mobile home

Q: I have an old mobile home that I would like to put a new roof on. I don’t want it to hold the weight of the roof, but am thinking more along the lines of a carport type roof over it.

A: What a great idea!  Putting a new roof on an older mobile home is a great way to prevent or stop any leaks, enhance the look of the unit and make it easier to cool and heat.  We have done many such projects and each one has presented its own little challenges.  It all depends on how tall you want to go with the new roof and what is allowed in your area but pre-engineered trusses are a very cost effective way to achieve this.

Depending on the age of the “mobile home” (accent on the mobile part), it was made to be light and mobile so everything is just adequate to support its own weight and that’s it.  The roof joists are tiny and smaller yet are the wall studs.  They will normally not be able to support any additional roof loads.  What we usually do is run some posts about every 10 feet and some beams on top of those, placed just outside your existing walls.  This way the roof is free standing and does not add any load to the mobile home walls.

With the new trusses in place, you may wish to install some form of insulation in the newly created attic space.  It doesn’t take much to get rid of the roof noise, keep things cool in the summer and toasty warm in the winter.  Put a nice shingle roof on with some gutters and suddenly you have a carefree roof system.

You can contact one of our sales representatives at 1-800-667-3511 and they would be happy to provide you with a competitive quotation.  They will discuss your current needs and possibly offer some great ideas too!

Ducting allowance: I-joists vs floor trusses over my basement suite

Q: While studying the plans of my proposed new house project, I find that I may have to ‘drop’ the ceiling in my basement suite to allow for dryer and range venting which will be running perpendicular to the 2×12 engineered I-joist direction of the main floor. Floor truss joist (parallel chord floor truss) may be my solution to keep the ceiling up where it belongs and run ductwork inside the framework of the trusses. My maximum span is 17′. Will floor trusses work for this span? What OC will be required? How will the ‘bounce’ factor on the main floor be affected compared to regular engineered I-joist?


A: I agree with you in not dropping the ceiling height in your basement.  Engineered I-Joists are a great choice for floors as they can achieve much greater spans than conventional lumber and their dimensional stability means little or no shrinkage.  This all contributes to a well performing floor system.

Though I-Joists can be drilled or have holes cut in them to accommodate plumbing and ducting at select locations, if you’re not sure of where the ducting will be or you would like to place it near the outer edges of the span, then a 4×2 parallel floor truss system is the way to go.  A large “chase” can be incorporated into the design with little or no effect on deflection or performance.  This opening allows for larger air handling vents too.

The webs in a 4×2 truss are usually installed at roughly a 45 degree angle which allows for the greatest amount of room between the members.  With this design, you could literally run your vents and ducting within a foot of the bearing walls if need. (Or practically any location in between for that matter).

We can span 17’ at 12” deep and still maintain a 24” o/c spacing.  Keep in mind that you will need to use ¾” plywood if that is the spacing that you want.

Bounce?  Sorry but if you’re looking for a trampoline, we don’t sell those!  All kidding aside, bounce or “deflection” is determined by several factors when designing a 4×2 floor truss.  BC Building Code requires a floor to perform at L/360 meaning that you would take “L” in inches and divide by 360.  This would give you the maximum deflection allowed in your floor system by code.  A 17’ span would work out to (17×12)/360 = 0.56 inches.  We try to design our I-Joist floors at L/480 which would limit your deflection to (17×12)/480 = 0.42 inches.  A 4×2 floor truss can easily exhibit numbers better than L/1000 or 0.20 inches.

One more thing to consider in design is vibration.  Long, slender floor members tend to vibrate under certain conditions and the I-Joist or floor truss design will address this factor.  I-Joists allow for bridging and strapping between them and 4×2 floor trusses allow for continuous “strongbacks” to be attached to the vertical members.  This can really strengthen up your whole floor design.

So, the choice is up to you.  I hope that I have addressed your questions but if not, please feel free to contact me directly should you have any more concerns.

Can you provide a “barrel” vault in a particular area of the roof?

Q: I’m looking for some different architectural features in my new home. Can you provide a “barrel” vault in a particular area of the roof?

A: Funny you ask!

I am just in the midst of designing a barrel vault roof system right now and you might be surprised at some of the possibilities!

There are several different options with the simplest being just a “bowstring” truss. This is where the top of the truss, or the roof section, is the only rounded part, with the ceiling remaining flat.

bowstring truss

Another option is where only the ceiling is barrel vaulted and the roof can be any other configuration.

barrel ceiling truss

And yet another, which is my favourite, the ceiling and roof are both barrel shaped.

barrel truss

The possibilities are really endless and the spans that can be achieved make this a very reasonably priced option. The biggest advantage to having roof trusses like this over say a conventionally framed barrel vault or Glulam beams, is that you can get so much more insulation into the roof cavity. There is no “steaming” of lumber to “bend” it, no expensive special order arched beams or any construction delays. We can build these right in our factory to your exact specifications and you can install them with very little effort.

My truss system above my garage is used for storage. My ceiling is starting to crack and I am concerned, what can I do in order to use the space for storage again?

Q: My truss system above my garage is used for storage. My ceiling is starting to crack and I am concerned about storing things up there now. I have some numbers on a truss 020022 / 30 / common. What can I do in order to use the space for storage again? I thought about using 3 – 28′ I-joists to support beneath the nail plate supported on each end.

What is your thought on this?


A: I always like questions people have about getting more out of there current truss design!

The first thing I would ask is whether or not your trusses were designed to support additional storage loads in the first place. The marks that you say are written on a truss really don’t help me too much but seeing that they are for a garage, I would imagine that they are just common trusses designed to carry only minimum snow and dead loads.

Placing any kind of additional load on a truss whether it is permanent or temporary, can adversely affect the performance of the roof system. Trusses are designed with safety factors which help them to survive occasional temporary overloading due to construction loads while being installed but, any kind of additional load that is applied long term will definitely affect the truss system and cause things like cracks in the ceiling.

If a truss is originally designed with extra storage capacity, then it will perform as intended and provide years of trouble free service. All trusses are engineered components and are far more complex in their design than simple rafters. For this reason they must not be altered in any way either by cutting, drilling or adding additional loads!

Now, to answer your question about what can be done to “stiffen up” your ceiling. Possibly adding more support under the trusses could be a solution but I doubt that a 28’ I-Joist would be a good choice. Again, I-Joists are an engineered product and must be designed to carry loads. As the I-Joist would be used in conjunction with the existing trusses, only an engineer would be able to help you with that solution. Possibly the self weight of the I-Joists might add to the problem. That is a very long span for an I-Joist and its deflection would be fairly high. This is what you are trying to correct – not make worse!

I would suggest that you remove as much of the “storage load” that you have in the attic to allow things to get back to normal for a bit, then call an engineer in your area that specializes in roof trusses and have him come out and take a look at your situation. He will be able to come up with a solution that can fix your problem.

I hope this information is helpful for you and that you can continue to enjoy your storage space – crack free!