Case Study Flashcards
What U-value does BR require for roofs?
0.18
What U-value does Passivhaus require for roofs?
0.1
When do you need building regulation permission for reroofing of a flat roof?
If you are to recover more than 25% of the area The performance of the new roof will be significantly different in the event of a fire You want to carry out structural alterations
When were system build houses typically constructed?
Between 1918 and 1980
What can Non-Traditional Houses be constructed of?
Steel Framed Pre-cast concrete In-situ concrete Timber Framed
Name some types of Non-Traditional Dwellings listed on the Designated Defective List? (Part of the Housing Act 1985)
Airey Orlit Type I Orlit Type 2 Wates
If it is not obvious externally if a house is steel frame, how would you find out?
Look in the roof space, the gable or flank wall normally comprises metal framing
What did you suspect was causing the deterioration of the concrete deck?
We didn’t commission any testing as part of the works. But I considered that it may have been likely the use of High Alumina Cement which was popular at the time of construction (between 1950-70). It was banned for use after the 70s due to a number of roof collapses due to vulnerability to chemical attack.
Why is HAC (High Alumina Cement) vulnerable to damage?
It’s more vulnerable in wet and damp areas, which correlates with the basement location. The concrete carbonates and therefore starts to corrode the reinforcement wires in the concrete joists and weakens the concrete.
How would you test for concrete carbonation?
You can spray the concrete with a solution that determines whether the concrete has carbonated. Any uncarbonated concrete changes to a magenta colour.
What causes carbonation?
Where Co2 combines with water and lowers the PH of the concrete and therefore weakening it.
Why were system builds used in construction?
There was a timber ban following the second world war and there was a housing shortage so building had to be fast and effective. They were only designed to be temporary
What minimum bearing would you expect joists/beams to have?
Typically 75-100mm Depending on whether the beam is supported by steelwork (75mm) or supported by masonry (100mm)
What is Type A Waterproofing?
Is a barrier system usually installed prior to construction. They historically would have used bitumen externally. Type A is known as tnaking and provides protection against ground water ingress by applying a waterproof material to teh external walls and floor slabs of a basement. The waterproofing material can be applied externally, sandwhiched or internally. Type A examples include; Bonded sheet membranes, liquid membranes, clay liners etc.
What is Type B Waterproofing?
Protection against water ingress which is provided by the structure.
Type B Protection relies upon the design and materials incorporated into the external shell of the structure itself. Structures that provide Type B protection should be constructed of reinforced water-resistant concrete or structural steel.
Type B designs place added importance on the design of the structure and the specification of materials as well as the quality of the workmanship involved in preparing and placing concrete. This is due to the fact that the pattern of any seepage encountered is often associated with poor joints, cracks or other discontinuities such as service penetrations.
What is a Type C System?
Protection against water ingress into usable spaces which is provided by the incorporation of an appropriate internal water management system.
Type C Protection offers a waterproofing solution by allowing groundwater to penetrate through the external wall or floor as far as the cavity between the external shell and internal lining/finishes, collecting it via a Cavity Drain Membrane and then diverting it into controlled drainage and a designated safe point of disposal.
Cavity Drain Membranes are studded on the external facing surface, allowing any water that penetrates the structure and reaches the membrane to flow into the designed drainage channels that carry the water to either a sump and pump chamber or away from the structure if passive drainage is possible.
What British Standard details tanking methods?
BS8102:2009
What’s the difference between a warm and a cold roof?
A cold roof has the insulation beneath the deck betweem or below the joists and needs to be ventilated. A warm roof has the insulation on top of the deck.
What is the maximum span and loading for Hollowcore Plank?
It depends on the thickness and the span. But for a 250mm depth as per the one originally specified, the span can go up to 10m. The imposed load can fluctuate depending upon the span and depth of the plank. For 250mm it varies from 0.75 to 15.00 KN/M2
What are the benefits of using Hollowcore planks?
They have good sound and fire resistant properties.
Fast and simple to erect.
Where hollowcore concrete planks are used as a roof deck option, what forms the remaining parts of the roof construction?
DPM, Screed, Waterproofing.
What was the system build of Block 03?
It’s unknown but looking at archive records and the characteristics of the building I think it’s likely an Orlit construction, or variation of.
What is the Orlit system?
It was a type of non traditional construction generally used for houses and flats between the 40s-50s.
They generally have a pre cast concrete frame with concrete facing slabs and a typically a flat roof, although can be pitched.
Defects: 0 only up to 30mm of concrete coever so prone to carbonation. Use of High Alumnia Concrete.
What did you include in the specification for the flat roof?
Specified the use of 75mm screed laid to a 1:60 fall
Waterproofing specified by others by included vapour control layer, 2 layers mastic asphalt (to 20mm), sand solar treatment.
Angle fillet to corner and then mastic chased in with concrete and pointing to existing DPC
