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Masonry work on The Grange chimneys

September 12th, 2010

Masonry work on The Grange chimneys

The masonry work on the two south chimneys and one of the west chimneys has been finished. The north east chimney is being rebuilt and is almost done. Scaffolding will be moved to the north west side of the building so re-pointing can be done on the final chimney. Caps and flashings will be added (see below) next.

Masonry work on The Grange chimneys

Structural engineers from Jewell Engineering have developed a strategy for shoring up the portico so that the foundation can be rebuilt. The entablature (the part of the portico above the columns) will be supported with a beam running from the steps foundation at the south side of the middle slab to the concrete part of the west side air duct. Then the slab and columns will be shored using steel angles at the edges of the slabs. Once this is done, the piers under the slab can be rebuilt and the foundations for the steps repaired and pointed.

A heritage construction moment.

Chimneys have developed and changed over the years but share a number of different parts—the stack, the flue, the wythe, the corbel, chimney pot, flashing, caps, and cowls. By the 19th century, the usual dimension for a brick flue came to be 9 x 9” or one brick by one brick. The wall between the flues, the wythe, was usually 4 ½” or half a brick. The north west chimney of The Grange, for example, has two whythes with the second wythe around the flue being constructed on edge.

As mentioned in previous blogs, water in concentration is extremely damaging. Corbels, or areas near the top of the chimney, were built out to shelter the lower sections from water. Unfortunately, they themselves collected water. Flashing, a type of metal skirt, is added to drain the water off. Chimney pots, or extensions to the flue, placed on top of the chimney, were an inexpensive way to extend the length of the chimney to improve the draft (or ability for smoke to exit). A chimney cowl can be placed on top to prevent birds and squirrels from nesting. They often feature a rain guard to keep rain from going down. A cowl might also be a wind cap that rotates to align with the wind and prevent a backdraft of smoke and wind back down the chimney. We will be closing the unused chimneys with a cap (see image below).

Masonry work on The Grange chimneys

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