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Memo to the Trudeau family: You’re smart to stay out of 24 Sussex Drive. Engineers say its walls might drop pieces of rock on those who live there.
Also, the walls have weakened enough to increase the chance of collapse in the event of an earthquake. Remember that day in 2010?
Overall, the outer structure of grey limestone walls is in “poor to fair” condition. Some bits are “very poor.”
The venerable building with the killer view of the river is a victim to time, but also to the original choice of poor-quality limestone for its walls, mortar that varied in quality, and sub-par workmanship decades ago.
In some places, the mortar never made contact with the stones it was meant to hold in place. Some interior gaps never had mortar at all, while mortar in other spots has crumbled away.
And some of the limestone blocks are now “disaggregated,” or cracking apart under forces that include repeated freeze-thaw cycles, like a road with potholes.
Walls are cracked in some places, bowed out sideways in others.
And when the new government owners did a major reno in 1950, they covered over old problems instead of fixing them.
Now a detailed report by Public Works and Procurement Canada provides a detailed look at the “exterior envelope and structure” of 24 Sussex for its owners, the National Capital Commission. Released through access to information, the report has repair cost estimates removed to avoid tipping off future bidders.
Overall, “the exterior walls are considered to be in poor to fair condition.”
Left untreated, it says, the accelerating deterioration of the prime minister’s official residence will cause “an eventual loss of the structural integrity of the wall(s).”
• Let’s start with those stone blocks. Most of the 1867 stones were quarried locally, a material called Gloucester limestone. But the report notes: “Gloucester limestone is known to be a poor quality building stone, and should not be used” in future work. (The material is used today for crushed stone.)
“A large quantity of the Gloucester limestone has become severely disaggregated with multi-directional cracking through the full body of the stone…
“The deterioration poses a health and safety threat to site occupants: fragments of the stones could easily dislodge and fall to the ground.”
The risk is greatest in spring thaw, as with potholes in roads, and is greatest on the home’s south and west sides “where site occupants can easily get close to the building walls.”
The walls aren’t likely to collapse, the report says, but the stones are so bad that if someone removes them to rebuild the wall, they are likely to “disintegrate.”
• Workmanship is a problem, too. The house was built in 1867, renovated and extended in 1909 and again in 1950.
“The workmanship of the 1950s and the earlier masonry work is not considered to be of particularly high quality,” the report says. For instance, they used mortar of varying qualities, “in some cases achieving little or no bond to the stone.”
And the 1950s workers left, in some cases, actual gaps between the stone and the mortar intended to hold it in place.
“The relatively poor workmanship of the 1950s masonry and mortar work will result in a reduced lifespan for the masonry walls.”
•”Significant cracking is evident at six locations on the building’s walls,” and the overall wall condition “varies from very poor to good.”
There is also bulging of the masonry on all four sides of the house.
Eight stone window lintels (the single stone pieces across the tops of windows) have fractured and seven stone sills have fractured.
• A lot of the masonry has crumbled away.
“Numerous open joints (between stones) were observed where all mortar has deteriorated and emptied: a mason’s slick could typically be inserted +/- 200 mm (millimetres) deep into the opening with no resistance.”
“The mortar joints at grade (ground level) are in very poor condition and are generally disintegrated and friable,” meaning they crumble when someone rubs or squeezes the material.
Even worse is the mortar below ground level, found to be “soft, easily removed by hand tools and reverting to sand.”
• Water is getting in and doing bad things, some of it caused by falling-apart gutters and downspouts that don’t drain away water. Moisture has corroded the steel ties that join the limestone to the cinder block wall behind it. And rusting steel lintels over windows are expanding, pushing against and cracking the masonry around windows.
For instance, steel lintels on the north side of the 1950s addition are corroded and this jacks up the wall above them. In addition, the limestone may no long be held in place because the steel ties behind it are corroded. No one can tell without opening up the wall.
If so, “this area of masonry may easily become unstable,” the report warns. It calls for more investigation.
And then there’s the earthquake risk. On paper it shouldn’t be too bad, the engineers say — but the reality is that since the outer limestone walls are no longer well connected to the supporting walls behind them they “may be vulnerable to out-of-plane collapse in an earthquake.”
(Out of plane means the sideways shaking of an earthquake makes a masonry wall bend sideways, and then collapse.)
• There’s some good news. The roof, rebuilt in 1998, is in good shape. So are the six-metre-tall chimneys.
But even with these, there’s a catch. Tall brick chimneys can snap off in earthquakes, and if the NCC decides to quake-proof 24 Sussex, it will have to dismantle the chimneys and rebuild them.
Jim Cowie, a Halifax engineer with experience in historic masonry buildings, says the damage can be fixed but it will be expensive.
He called the building “sadly neglected.”
“It can be fixed. It’s just a matter of putting dollars to it. Plus it’s heritage, and once it becomes heritage there are things you just can’t do,” which includes demolishing and rebuilding from scratch, he said. “No way would they tear this down.”
And he said the costs will rise if heritage rules require the new limestone, mortar and windows to have the same look as the originals.
He noted that the Public Works study still hasn’t examined the inner part of the walls behind the limestone, so there are still unknowns about how much needs to be fixed.
There is still no formal proposal to repair 24 Sussex.
A few weeks ago, the NCC’s CEO, Mark Kristmanson, told this newspaper: “We continue to work with the government on 24 Sussex Drive. I can’t really say very much about it except that I’m encouraged by some of the work our teams have been doing to arrive possible solutions to move the project forward, so we are looking forward to having an opportunity to share those.”
tspears@postmedia.com
twitter.com/TomSpears1
查看原文...
Also, the walls have weakened enough to increase the chance of collapse in the event of an earthquake. Remember that day in 2010?
Overall, the outer structure of grey limestone walls is in “poor to fair” condition. Some bits are “very poor.”
The venerable building with the killer view of the river is a victim to time, but also to the original choice of poor-quality limestone for its walls, mortar that varied in quality, and sub-par workmanship decades ago.
In some places, the mortar never made contact with the stones it was meant to hold in place. Some interior gaps never had mortar at all, while mortar in other spots has crumbled away.
And some of the limestone blocks are now “disaggregated,” or cracking apart under forces that include repeated freeze-thaw cycles, like a road with potholes.
Walls are cracked in some places, bowed out sideways in others.
And when the new government owners did a major reno in 1950, they covered over old problems instead of fixing them.
Now a detailed report by Public Works and Procurement Canada provides a detailed look at the “exterior envelope and structure” of 24 Sussex for its owners, the National Capital Commission. Released through access to information, the report has repair cost estimates removed to avoid tipping off future bidders.
Overall, “the exterior walls are considered to be in poor to fair condition.”
Left untreated, it says, the accelerating deterioration of the prime minister’s official residence will cause “an eventual loss of the structural integrity of the wall(s).”
• Let’s start with those stone blocks. Most of the 1867 stones were quarried locally, a material called Gloucester limestone. But the report notes: “Gloucester limestone is known to be a poor quality building stone, and should not be used” in future work. (The material is used today for crushed stone.)
“A large quantity of the Gloucester limestone has become severely disaggregated with multi-directional cracking through the full body of the stone…
“The deterioration poses a health and safety threat to site occupants: fragments of the stones could easily dislodge and fall to the ground.”
The risk is greatest in spring thaw, as with potholes in roads, and is greatest on the home’s south and west sides “where site occupants can easily get close to the building walls.”
The walls aren’t likely to collapse, the report says, but the stones are so bad that if someone removes them to rebuild the wall, they are likely to “disintegrate.”
• Workmanship is a problem, too. The house was built in 1867, renovated and extended in 1909 and again in 1950.
“The workmanship of the 1950s and the earlier masonry work is not considered to be of particularly high quality,” the report says. For instance, they used mortar of varying qualities, “in some cases achieving little or no bond to the stone.”
And the 1950s workers left, in some cases, actual gaps between the stone and the mortar intended to hold it in place.
“The relatively poor workmanship of the 1950s masonry and mortar work will result in a reduced lifespan for the masonry walls.”
•”Significant cracking is evident at six locations on the building’s walls,” and the overall wall condition “varies from very poor to good.”
There is also bulging of the masonry on all four sides of the house.
Eight stone window lintels (the single stone pieces across the tops of windows) have fractured and seven stone sills have fractured.
• A lot of the masonry has crumbled away.
“Numerous open joints (between stones) were observed where all mortar has deteriorated and emptied: a mason’s slick could typically be inserted +/- 200 mm (millimetres) deep into the opening with no resistance.”
“The mortar joints at grade (ground level) are in very poor condition and are generally disintegrated and friable,” meaning they crumble when someone rubs or squeezes the material.
Even worse is the mortar below ground level, found to be “soft, easily removed by hand tools and reverting to sand.”
• Water is getting in and doing bad things, some of it caused by falling-apart gutters and downspouts that don’t drain away water. Moisture has corroded the steel ties that join the limestone to the cinder block wall behind it. And rusting steel lintels over windows are expanding, pushing against and cracking the masonry around windows.
For instance, steel lintels on the north side of the 1950s addition are corroded and this jacks up the wall above them. In addition, the limestone may no long be held in place because the steel ties behind it are corroded. No one can tell without opening up the wall.
If so, “this area of masonry may easily become unstable,” the report warns. It calls for more investigation.
And then there’s the earthquake risk. On paper it shouldn’t be too bad, the engineers say — but the reality is that since the outer limestone walls are no longer well connected to the supporting walls behind them they “may be vulnerable to out-of-plane collapse in an earthquake.”
(Out of plane means the sideways shaking of an earthquake makes a masonry wall bend sideways, and then collapse.)
• There’s some good news. The roof, rebuilt in 1998, is in good shape. So are the six-metre-tall chimneys.
But even with these, there’s a catch. Tall brick chimneys can snap off in earthquakes, and if the NCC decides to quake-proof 24 Sussex, it will have to dismantle the chimneys and rebuild them.
Jim Cowie, a Halifax engineer with experience in historic masonry buildings, says the damage can be fixed but it will be expensive.
He called the building “sadly neglected.”
“It can be fixed. It’s just a matter of putting dollars to it. Plus it’s heritage, and once it becomes heritage there are things you just can’t do,” which includes demolishing and rebuilding from scratch, he said. “No way would they tear this down.”
And he said the costs will rise if heritage rules require the new limestone, mortar and windows to have the same look as the originals.
He noted that the Public Works study still hasn’t examined the inner part of the walls behind the limestone, so there are still unknowns about how much needs to be fixed.
There is still no formal proposal to repair 24 Sussex.
A few weeks ago, the NCC’s CEO, Mark Kristmanson, told this newspaper: “We continue to work with the government on 24 Sussex Drive. I can’t really say very much about it except that I’m encouraged by some of the work our teams have been doing to arrive possible solutions to move the project forward, so we are looking forward to having an opportunity to share those.”
tspears@postmedia.com
twitter.com/TomSpears1
查看原文...
