Tuesday, June 23, 2009

Well, we're moving on up (moving on up)...

I saw an interview with Norman Lear the other day so today's title goes back to one of his classic shows...

And we are moving up...onto the roof of the Amstel House to do some work on a different chimney before beginning roofing at the Amstel House. We're also goi
ng to start roofing the Dutch House. The hearth will wait...

Here's what we discussed at out meeting on June 15 (included were the architect, mason, general contractor, and roofing subcontractor):

The kitchen chimney is complete and we are very satisfied with the final result. So should the mason's begin working on the fireplace and hearth? Not yet. We have another chimney on the house that needs work. If you're familiar with the Amstel House, it's the chimney that had the trees growing out of it - 'nuff said.

The tree (actually 2 trees) were cut out of the chimney by the masons. The chimney itself needs to be completely re-pointed. There are also several severely deteriorated bricks that need to be replaced, the very top of the chimney needs to be rebuilt so correct bricks that have shifted or are missing, and the caps (currently flagstone) need to be installed correctly or replaced. It's going to be a project that will take a few days to complete. It will require some historic brick (luckily we have extra from our first chimney project), and we'll use the same mortar mix on this chimney. Here's a pic of the current state of affairs on one side of the chimney - the other sides aren't any better:

Now, before we started anything we knew that this chimney was going to need some work so our architect included the work on our initial drawings for the kitchen chimney and roofing projects. We had the whole lot approved by the HIstoric Area Commission at the same time so we could get one permit to cover everything. We weren't absolutely positive that this chimney was going to get treated in this phase though...it really depended on how we were doing compared to the project budget. I'm happy to report we are well under-budget which allows us to do this much needed work too.

We need to complete this chimney work before putting a new roof on the kitchen wing at the Amstel House to prevent any damage to our brand new roof from scaffolding or walking/standing on it. Since our roofers are ready to get rolling, we are going to have them start working on the Dutch House first, then work on the pent roof on the 4th Street facade of the Amstel House then finally move to the kitchen wing. That should allow our masons plenty of time to finish up the second chimney. Once the roofers start on the kitchen wing, the masons will return to work inside on the fireplace and hearth.

Besides timing of work, we also discussed some roofing details. One of the main questions for the roofer was whether they were comfortable with our mason's suggested flashing detail. It's totally up to them since they need to warrant the work. After discussing it back at their office, they decided that they would prefer to go with our original flashing plan so that's what we'll do.

We also discussed how to handle the ridge detail. Before getting into that though I should explain the roofing system that we're planning to use.

Since we may be using our kitchen fireplace in the future, and since our neighbors may use their fireplaces as well, we want our wood roof to be as resistant to fire as possible. To get the highest fire rating (Class A)for a wood roof, you need to use wood shingles that are treated chemically with a fire retardant to give them a class B rating, and use fire retardant plywood as sheathing beneath them. Since wood shingles should never be applied directly to a solid sheathing like plywood because the shingles require airflow directly beneath them to prevent rot, we will use a product called "Cedar Breather" to allow ventilation between the shingles and the plywood. For a detailed discussion of this installation, fire ratings, and everything else you'll want to know about cedar roofs visit the website of the Cedar Shingle and Shake Bureau (it's good to remember that this Bureau is an industry sponsored organization).

I have to admit that I was reluctant to use the Cedar Breather product for fear of not providing enough ventilation beneath the shingles. I did a bit of googling to look for preservation projects where the breather was used. The only well-documented project I found was a 1997 roofing job at the Chowan County Court House in Edenton, NC (Check it out here). I contacted the engineers that designed the roof to find out if they had experienced any problems attributable to insufficient ventilation. They have had no issues - so it has at least a 12-year track record. Our architect and general contractor also have used the product on preservation projects in the past and have been pleased with the results so Cedar Breather it is. (For more information on Cedar Breather visit the manufacturer's website here.)

At the ridge of the roofs we will use a Boston Ridge with an vapor-permeable ice & water shield beneath the shingles, and the cedar breather beneath the shield as illustrated here. This will allow air to escape from the attic, while insuring that the ridge shingles can still breathe. Without a ridge vent humid air will be trapped in the attic and cause the roofing system to fail prematurely through rot.

All of this would be a non-issue if we were content with a Class C fire rating that can be achieved by treating the shingles and applying them in the historic manner - directly on shingle lath. Applying directly to lath that is appropriately spaced allows excellent ventilation. It's a system that has performed well for hundreds of years in the U.S. (with the exception of roof fires).

Enough about that...The roofers provided us with shingle samples so we could approved them before work begins.

These are for the Dutch House. They are sawn on both sides, 7/8" thick at the butt, and have a bevel cut on the end to match the existing Dutch House shingles.
In the 18th century, shingles were split by hand using a tool called a froe. Then the shingle surfaces were smoothed, or dressed, with a drawknife. While we could do that today, we decided instead to use sawn shingles which still have smooth surfaces though may show some saw marks. An option that is, in my mind, definitely not appropriate are modern shakes that attempt to mimic a hand-split appearance and are often marketed as appropriate for historic buildings. They are what's on the Dutch House now. I think they are too primitive looking for a middle class, urban artisans house which is what the Dutch House is.

As you can see in the photo, they are slightly thicker than the existing Dutch House shingles which is fine with us and will make them last longer. You'll notice that one of the shingles is very wide (11"), and we don't want to use it as is. A shingle this wide will need to be ripped (sawn along its length) to make it no more than 9" wide. Smaller widths help prevent the shingles from splitting or cupping over time.

These are for the Amstel House (below). They are standard "Royals" - 24" long, 1/2" thick at the butt, and clear (no knots or other imperfections):

We also asked the roofers to provide us with a copy of the label that certifies the fire-treatment on the shingles, and the material safety data sheet. If you are installing a wood roof, particularly on that has been treated with either a fire retardant or a preservative to prevent fungal decay (you can't do both treatments - they're incompatible chemicals), you should ask your roofer to provide you with this information and keep it in your project files. Here's a pic of our shingle label (faxed copy):

They also provided us with samples of the ridge cap that they'll use on the Amstel House (It's pre-made), the Cedar Breather, and the ice & water shield. The ridge cap for the Dutch House will need to be made on site by the roofer.

The roofers are supposed to start at the Dutch House on Monday June 22, and the masons at the Amstel House on Tuesday June 23. Before the roofers get started at the Dutch House, I'll need to get in there and secure anything that might be damaged by vibrations caused during hammering.

That wraps up a nice long post! Talk to you next week when the roofers and masons arrive!

No comments:

Post a Comment