In this third article in our series, and as part of our PFI special, David Weight of Currie & Brown looks at the differences in lifetime costs between deep-plan, shallow-plan or courtyard-based hospital designs
The design of hospitals is currently in a state of flux. For a start, the design of health buildings, fuelled by debate over the first PFI hospitals, has revealed a tension between economy of plan and operational flexibility for the healthcare provider, against quality of environment for all users of the building, particularly patients. In terms of building design this is characterised as a choice between shallow and deep-plan hospitals. There has also been the introduction by the government of minimum standards of service in hospitals, which have been reinforced by evidence of causal links between indicators such as recovery times, cross-infection rates and re-admission rates. This impacts on hospital design – for example, the preponderance of single bedrooms.
The challenge for hospital design is that the lessons of emerging research are recognised but the funding for the capital and operational on-costs of these lessons isn’t yet available. Meanwhile, those responsible for capital investment decisions increasingly see the need to meet anticipated future change without major capital penalty. Because of the impact these factors can have on building form choices need to be made early on, during the option appraisal stage of the capital planning process.
This article examines indicatively the in-patient environment and reviews configurations responding to existing common types. It then uses Currie & Brown’s Live Options software tool to examine a range of capital and operational indices to draw out the areas of discrimination between design choices, including an attempt to put a price on the options that lend themselves to greater future flexibility.
Live Options: The whole-life costing computer model
The whole life costings presented here are based upon Currie & Brown’s Live Options software, which is an integrated suite of geometric, engineering and energy calculation programs. Whether the development is an office, school, hospital or warehouse, the process starts in the same way, by using a basic but specific design template. This is modified to incorporate, say, changes in the size, shape and operational performance.
The program integrates fabric and building services components and can show how costs change when a building element is changed, such as increasing the proportion of glazing in the facade. It does this by providing a detailed breakdown of changes and shows the capital costs of physical items and the effect these have on building performance. Any changes to heating and cooling loads will be quantified in terms of the effect this has on chillers and electrical supply loads, for example.
Changes to the energy profile of the facility are also calculated. The program uses this data to assess the cost-effectiveness and overall viability of alternative solutions when considered against the facility’s projected economic life.
The model also takes account of repair and maintenance costs. This includes regular inspections, planned and unplanned maintenance and replacement costs for individual building components. These costs are automatically incorporated into cash flow, discounted and summarised and net present costs are shown against each component, which assists in making choices and in value-engineering.
Our base building
Shown right are the typical capital, energy and repair and maintenance costs for a very conventional hospital ward extension of 9000 m2 gifa. It is not air-conditioned, but 50% of the area needs mechanical ventilation. Circulation area makes up 28%, which includes four stair shafts and four lift shafts. It is four storeys high, and deep plan, being 22.5 m between parallel external walls. It is supported by an insitu concrete flat slab frame with a grid of predominantly 7.5 × 7.5 m.
Overleaf we show the increases or decreases in those costs when this hospital is remodelled into first a shallower plan building and second when it is arranged as two blocks wrapped around small courtyards.
Scenario one: Changing the ward from deep plan to shallow plan – capital costs
This change enables certain areas, such as the reception, to have daylight and a view. Surprisingly, the area of corridor turns out to be very similar. This is because although the spine corridor length is longer, the turns off it to rooms are reduced, and so the gross floor area and net area are just about the same, with circulation still at 28% of the gross floor area. Natural ventilation is adequate for greater proportion of the building’s reduced depth, so the proportion needing mechanical ventilation reduces from 50% to about 38%.
Modelling required the following inputs:
- The average depth on plan was changed from 22.5 m to 15 m;
- Rates for formwork increased;
- Proportion of area needing mechanical ventilation reduced from 50% to 38% and rate reduced to reflect shorter runs;
- Shading factor restored to reflect 10% more sun where facing the existing building. (The base model had a shading factor knocking down the solar effect by 10% because it was closer to the existing building.)
Changes in capital costs
Taking the main elements in order as they appear on the graph:
- Substructure Piling increases slightly, as there are more column points and more external envelope to carry, although the weight changes little (green). There is an increase in the external girth of the building, which increases lengths of grounds beams and walls between ground beams up to dampproof course (blue).
- Structure The frame costs increase as the construction, or formwork particularly, is less efficient. Also there is a greater length of perimeter beams.
- Envelope The main effect here is the increase in the external girth and area of vertical envelope, including eaves and gutters to roof (red), walls (blue), windows (yellow) and external shading (pink).
- Internal division The girth of internal walls is reduced. Red is load-bearing walls, green is non-load-bearing walls, and pink is saving on fire compartmentation in ceiling voids. Doors are unchanged.
- Internal finishes Areas of drylining to external walls has increased (red).
- Mechanical The heating load has gone up (blue) in response to the increased area of envelope and its associated heat losses. Also the girth of perimeter heat distribution has increased. (The impact of envelope area on energy has reduced as U-values have been improved.) Mechanical ventilation (pink) is reduced, as more area is able to benefit from natural ventilation.
- Electrical and communications The extra heating load and external girth impacts on the pumps and electrical load (red). The security installation increased slightly, since part of its cost is geared to the building girth at the lower levels (light blue).
- Builders’ work Shown as a saving in light blue, this is based on a percentage of the services, and preliminaries are also based on a percentage. The effects on external works could be considered, but have been excluded, as this is site-specific. Preliminaries (red) are normally based on a simple but consistent percentage for strategic modelling purposes, although more refined methods may be used instead. Profits and overheads (light blue) are based on simple but consistent percentage allowances, although more refined methods may be used instead.
Scenario one: Changing the ward from deep plan to shallow plan – energy costs
Changes in energy costs are illustrated in the table. Prices for fuels are taken as 6.5p/kWh for electricity and 2p/kWh for gas, which is used for heating. To explain the main changes:
- Fabric losses increase according to the extra girth and area of envelope.
- Solar gains provide some compensation for the extra window area. (It is assumed that thermostatic valves are used so that gains reduce the heat demand.)
- Ventilation fans are reduced.
- Pumps and controls increase in response to the increased cartilage.
- Lighting use reduces in response to improved daylight factors created by the narrower form. This assumed that we have daylight-sensing controls on the lighting, or that occupants are vigilant in switching off lights when daylighting is adequate. A small amount of the energy used for lights will supplement the heating load slightly in the heating season, so this is also reduced. It should be noted that a third of the saving on lighting resulted from the taking out the shading factor.
- Air infiltration losses have been ignored in this study, since this will always be less that the required air supply rate. Infiltration losses outside of the occupation period are always unwelcome, but since hospitals are occupied continually, this is not an issue. If the building were entirely mechanically ventilated, air infiltration would be treated as an extra loss, since this air circumvents heat recovery measures.
Scenario one: Changing the ward from deep plan to shallow plan – repair and maintenance costs
The changes in net present costs over 30 years, discounted at 3.5% a year, are limited to the principle elements that change.
The maintenance of gutters, balustrading to roof, window cleaning equipment, walls and windows all increase with the extra cartilage of the building.
The increase in envelope area and therefore fabric losses has increased the heat capacity and associated maintenance and replacement costs.
Internal partitions reduce as external walls increase.
The light fittings are assumed to last a bit longer, as they will be switched on less often because of improved daylight factors, although the relationship between lamp usage and life is not linear.
Mechanical ventilation is less extensive and duct runs are shorter.
Over 30 years the combined effect for a change from deep-plan to a shallow-plan naturally ventilated hospital ward extension are:
Capital cost changes £705,000
Energy cost changes –£25,000
Maintenance and replacement changes£153,000
Total change in net present cost £833,000
Note about scenario one
Live Options has assumed the same proportion of the facade of this shallow-plan scenario is glazed as the deeper plan base building. Of course this increases the daylighting factor considerably. There are areas where the proportion of glazing could be acceptably reduced yet providing better day-lighting than the base scheme. This would reduce the cost of the shallow plan scheme.
Scenario two: Changing the ward from deep plan to one with two courtyards – capital costs
This change also allows more daylight to enter the building via the courtyards. This enables certain areas, such as reception, to have daylight. The circulation area has increased, so gross floor area has also been increased slightly in order to maintain the accommodation and net area. The gross floor area increases by the area of one structural grid, or 56 m2 to 9450 m2, in order to maintain the net area. Modelling required the following inputs (the colours used represent the same elements as in the scenario one graph):
- Increased gifa from 9000 m2 to 9450 m2.
- Reduction in net to gross ratio to maintain the same net area and reflect the increased circulation.
- The average depth on plan was changed from 22.5 m to 37.5 m, but an extra for undulations and bays was entered to reflect the overall girth of two times 150 m for both blocks.
- Two courtyards of 112 m2 were added, being twice as long as they are wide.
- The length of the join to the existing hospital was reduced.
- Shading was increased to reflect the fact that daylighting from the courtyards would not be as high as from the other windows and even a bit worse than from the courtyard of the deep-plan option.
- Mechanical ventilation is reduced to 34% as a response to the increased external wall and window area.
- The number of rooms and doors remains similar; the internal division is automatically reduced as external walls are increased.
Changes in capital costs
The costs here show the effect of a 5% increase in gross floor area, as well as the change in shape. Although the magnitude differs, the trend and explanation is similar as for the shallow-plan scenario. This option is disadvantaged by the comparatively small link to the existing building, which provided a big saving of envelope on the first two options.
Scenario two: Changing the ward from deep plan to one with two courtyards – energy costs
Some changes, pumps and parasitic loads, are driven more by the extra 5% gross floor area than by the extra external wall.
The explanation of other energy changes is similar to that for the change to shallow plan, given above.
Scenario two: Changing the ward from deep plan to one with two courtyards – repair and maintenance costs
The explanation of changes in maintenance and replacement costs due to shape changes are similar to that for the change from deep to shallow plan. However, these changes overlap with effects due to the increased area. For example, lighting use is again assumed to reduce and lamp lives are 10% longer, but the extra area cancels out this saving.
Over 30 years, the estimated combined effect for a change from deep plan to two squarish plans around a courtyard, are:
Capital cost changes £1,895,000
Energy cost changes £19,000
Maintenance and replacement changes£250,000
Total change in net present cost£2,164,000
Funding issues and the possible influence on design
The funding of mechanical ventilation raises a concern with the NHS departmental cost allowance guides method of funding. In England and Wales, allowances based on departmental costs are added to for site conditions and a number of other “abnormals” allowances. These include deep-plan ventilation. If one reduces the building depth and thereby saves on mechanical ventilation, the savings should transfer to the building envelope, but this is not the case.
Another concern is sloping sites, the foundation costs for which can be reduced by having shallow-plan designs laid parallel with the land contours. Deep-plan buildings which follow the land slope will tend to have more retaining walls and ramps. Alternatively, if a big cut and fill exercise is carried out to create a flat site, the volumes and cost will be greater for deep plan designs than for shallow plan designs. However, extra foundation costs caused by sloping sites is funded from the “abnormals” pot.
In conclusion, both the funding of deep-plan ventilation, and of foundations to cope with sloping ground, cause a funding bias towards deep-plan designs.