Foam Core: EPS, XPS, and Polyurethane

I am traveling deep into the heart of SIP country, to the New Englandshire of Brattleboro Vermont. It’s cold, it’s snowing, and it’s progressive. It’s the perfect storm for stress on a residential structure. Why? Because cold conditions create a large temperature difference between indoor and outdoor spaces and this is when condensation happens inside walls (read rot). Also, when it’s snowing we are less likely to be tramping around outside checking on the condition of our houses. And finally, progress is change and change causes us to operate outside our comfort zone and knowledge base.

Of course change is good. Otherwise we would still be building like this.

 

There are three basic materials used as the foam core of Structural Insulated Panels. Each of the three core materials have different advantages.

Polyurethane

Outside Brattleboro, Winterpanel has been making and testing polyurethane panels for over three decades. The main advantage of polyurethane (or the much harder to pronounce derivation, polyisicyanurate) is that it has the highest R-value of any SIP panel. After what’s called thermal drift, it’s about 6 to 6.8 of R-value per inch of panel.

The other advantage is that it has an extremely high melting point. Effectively if your house caught on fire, the polyurethane foam core would be one of the last things left standing.

The main detractor of urethane panels is the cost. Doug Anderson from Winterpanel says the difference is about 40 cents a square foot of panel. The other disadvantage in terms of construction is that  polyurethane has a high melting point, hot wire burners (the primary method of modifying EPS and XPS panels on site) can’t be used. This is not insurmountable but still something that needs to be addressed in the planning stage.

Expanded Polystyrene (EPS)

Winterpanel also makes EPS core panels. Over 80% of the SIP panels installed are EPS. EPS core material is widely available. It is easy to modify on sight and most sip installers have experience dealing with EPS. It’s also the least expensive option in terms of material cost.

All good things come at a cost. EPS core material has the lowest R-value and has a low melting point. That means if the fire in your house is intense enough to burn past the gypsum and the OSB–POOF! The good news is that if the fire gets that hot to begin with, most likely everything else inside your house is already charcoal.

 

Expanded Polystyrene (XPS)

Bo Foard of Foard Panel has been in the SIP business for over twenty years. He has made and installed Polyurethane, EPS and XPS panels and is convinced an XPS core is the best option in most situations.

XPS has many of the best characteristics of both polyurethane and EPS. It has a high R-value (5 R-value per inch of panel). It is dense and stable yet has a relatively low melting point so on-site modifications are as easy as EPS. Also, like EPS, it bonds easily to OSB and gypsum board.

Unfortunately XPS is expensive and manufactured panels are not widely available (the only manufacturer I could find that makes XPS panels as part of their regular panel line is Foard Panel other companies like Murus will make them when customers requests it.). The good news is that the folks at Foard seem to really know their stuff. We sat down for a good three-hour geek-out session on building science and I get the feeling that Bo and his project engineer Paul Malko could have gone on much longer.

As always I invite you to post a comment with your thoughts and insights about SIPs.

Better yet, go to the link at the top right of this page and Post Your SIP House.

Pictures from today

Get a Grip on Plumbing

I’ve still got some questions about plumbing.

 

I have asked several different SIP installers and manufactures about how to deal with the issue of plumbing and the standard response is; don’t put plumbing in exterior walls. That is pretty sound advice even if you live in the half of the country that allows it in the code.

Plan your house accordingly and you shouldn’t have any problems right?

 

But what about venting?

Again the answer is planning. I called my local plumbing source, Ed Cunha, who lives on the Cape. He said that if I’m not a…, um if I’m pleasant to my building inspector, he will probably say minimum pitch is ok (2-by block on one end and half-block in the middle). That means, in the space between the floors or inside walls, I could collect all my venting into one three-inch pipe (provided I don’t have seventeen bathrooms) and then turn it vertical. This way I’d only put one penetration through my SIP roof. If the pipe is going to be easily seen from the ground, Cunha will use copper to dress it up a bit.

On another note, some people have asked me what it is really like to work at FHB. Short answer: Great!

And as far as all the free stuff floating around, take a look at these shwag stacks.

 Free shwag:  All you can take

Not-free shwag: Testers only then this stuff goes back

 

It Takes a Team

My thanks to the SIP School Team.   

 

As much as I’d like to, the demands of my job don’t allow me to attend SIP school every week so I won’t be able to post every day. But that doesn’t mean the site has to suffer.

Go to the link at the top right of this page and it explains how to post your own house on this site.

If nothing else,  it might serve as a collection of SIP houses that anyone can look at.

Lifting SIPs

Dump ’em, stage ‘em, stack ‘em.  Lift, tilt, or tackle em. Whatever way you do it, the reality is that moving SIPs around the job site efficiently and safely is crucial to a successful install.

At the school we had the advantage of extra bodies. More people than you would ever need.

We also got certified to use a Class 1 forklift.

Cobb took this picture of me after I completed my certification test.

Do you need to get a crane like this?

Or will a fork lift do it?

A four-wheel-drive forklift will go a long way on most job sites. But an important thing to remember is that if the lift is undersized, it’s less versatile during staging and preassembly, and ultimately the install might take longer. If it runs over by a day, it might have been better to spring for a bigger lift and get the job done faster.

There are a lot of site specific variables, but basically the professional builders at the school were in two camps; those that like to do as much preassembly as possible and therefore had more demand for bigger equipment.  And there were those that like to put up one panel at a time and make adjustments along the way. In the end, it came down to what people felt most comfortable with.

I felt pretty comfortable sitting in the driver’s seat of the big crane

 

There are a few ways to attach the panels.

One way is to simply wrap the strap around the panel. This is used to get stacks of panels off the truck but won’t work for install because the straps get in the way when it’s time to fit the panels together.

The most common method is to attach a plate to the skin.

We used this method both to stand walls.

And to fly in roof panels.

Peter Bergford, who is a builder in Olympia Washington, said he uses his CAD program to pinpoint exactly where to locate the plates so the panel hangs at the right roof pitch.

Hooks are the other way to fly.

And they are fast. Just stab them in…

and let ‘er rip.

Not exactly. Cobb makes his own hooks and also sells them at $500 for a set a four with straps. Each panel gets four hooks, two long and two short, oriented towards the center. When the crane lifts them up they bite in and are secure.

Later he goes back and foams the hole when he foams the seams.

Show time

 

How hard was the certification test?

Disodium octaborate tetrahydrate. This was an answer that I got right. This is also called a borate and is used to discourage insects from using the EPS foam as a house. It’s pretty harmless stuff that is also used in talcum and baby diapers.

Pentane gas. I couldn’t remember this one. It’s the expanding agent used in the manufacture of EPS SIPs.

What’s next?

 

Back to work.

How to Wire SIPs

You’re going to take the leap and build a SIPs house.  Everything is set; manufacturer, dealer, designer.  Even your architect thinks it’s a good idea after you agree to supply him with a month’s worth of espresso.

 

 

 

 

You were lucky and lined up the subs ahead of time.  The roofing, siding, flooring, and concrete contractors all said they had been looking for the opportunity to work with SIPs.  Even better, your HVAC guy has already cut his teeth on three SIP structures and is fully on board.

 

Now all you have to do is line up an electrician.

 

A big question with SIPs is how do you make the electrical connection?  Unfortunately for you, the SIP industry has a bad wrap when is comes to running wire.  Is this reputation deserved?  If the electrician shows up on the job without a good understanding of wiring panels and/or the installers don’t help him out by communicating with him, the job is going to be a nightmare and that electrician will blame it on SIPs instead of where the real blame belongs (frankly that’s you).

 

 

The general contractor is responsible for making sure the SIP installers and the electricians communicate so that the electrician knows what tools he’ll need and has the information to do the job well.

 

 

If you build a SIP house, it’s all on you.  But luckily, prepping a SIP house doesn’t take much time if you make it part of the install. The tools you’ll need aren’t that expensive or hard to operate.  And, if done right, the proper electrical prep, will save you tons of aggravation down the road.

 

 

Who’s smiling now?

 

 

Here’s how to do it.

 

 

First, find out what your SIP manufacturer will do.  Most have horizontal and vertical chases but they may also add chases for a nominal charge based on your design.  This will save a bunch of time later on.

 

 

Second, become familiar with a few tricks that will make the installation a breeze.

 

 

The Hot Ball

 

Buy a ball bearing from a local machine shop. EPS panels will turn to vapor under very high temperatures.

 

 

 

 

 

Heat up a the ball with a torch.  You want the color to be just under red.  At this temp the ball will move through the foam but not cause a flame.

 

 

Drop it in the hole and watch it disappear.

 

 

Create a funnel for it to escape.

 

 

Presto chase.

 

 

 

Don’t touch it!

 

Standard auger

 

For short distances, you can plunge holes with a big auger.

 

 

 

If you’re using this hog, hold on tight.

 

Flex bit

 

 

A flex bit is your biggest friend for long runs.

 

 

Clearly identify where you need to go and angle it in.

 

 

 

 

Bingo.

 

 

 

 

This connector hole can be filled later.

 

 

Crane time

 

 

 

The rest of the flipbook

 

 

 

 

Now it’s time for some real fun.

 

 

 

 

 

R&R