Solid timber buildings enter the 21 st century aided by technology and environmental awareness.

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1 Solid timber buildings enter the 21 st century aided by technology and environmental awareness. Jeff Parker Lockwood Group Ltd and Member of Solid Wood Building Initiative. Abstract. Buildings made from solid timber walls have been with us since the middle ages, and industrialised systems have been in New Zealand since the 1950 s. Over 40,000 solid wood homes have been built in New Zealand. Log homes have a significant place in North American building. In 2006 the Department of Building and Housing had proposed removing the Schedule Values of thermal envelope insulation requirements for Solid Timber Walls from the Acceptable Solution of clause H1 of the Building Code. The perception had been that solid timber buildings were old technology and.insignificant in relation to the total number of homes built in NZ.. A consortium of manufacturers formed the Solid Wood Building Initiative and commissioned research to verify the properties of solid wood buildings met the energy efficiency requirements of the New Zealand Building Code. This research was also able to quantify some of the hitherto anecdotal information regarding humidity control, temperature control and indoor air quality benefits of solid timber homes. Outcomes were:- 1. the thermal mass of timber in solid wood homes was found to be significant 2. tables were developed for minimum insulation values for solid wood buildings and these were included in the revision of NZBC clause H1 Energy Efficiency 3. solid wood houses were shown to effectively increase the percentage of time such areas as bedrooms remained within preferred humidity levels 4. heat energy produced by wooden materials absorbing and desorbing moisture did act to heat on cold days and cool on hot days, but the effect was small. Keywords. Solid wood; thermal mass; humidity

2 Introduction. Solid timber homes are made in New Zealand by a number of manufacturers. Four of these manufacturers, Fraemohs Homes, Intalok, Organic Buildings and Lockwood formed the Solid Wood Building Initiative (SWBI). This was timely in that Department of Building and Housing was about to revamp clause H1 of the Building Code; that relating to energy efficiency in homes. Compliance with H1 can be met by satisfying the Acceptable Solution H1/AS Until October 2007 this clause called up Tables for minimum insulation values for walls, roofs, floors, joinery from NZS 4218:1996 TheDBH proposal was to change the thermal insulation reference from NZS 4218:1996 to NZS 4218:2004 then revamp Table 1 in NZS 4218:2004 by increasing the minimum R values required for the building thermal envelope components of non solid buildings. However they also proposed removing Table 2 which was the minimum R values for solid construction and replacing it with a Table for solid construction (excluding timber). The previous tables had been included because of historic use and the feeling that solid timber houses were warmer than timber framed houses of the same era, ie little or no insulation. In fact, in the 1960 s and 1970 s solid timber homes were sought after because they had higher thermal insulation values than uninsulated timber framed homes. However as builders, customers and regulators started to specify at least some minimum levels of thermal insulation in their buildings then the obvious advantage enjoyed by solid wood buildings was diminished. After initial talks with some solid timber housing manufacturers, the idea of removing the Table for solid timber construction was dropped, and DBH proposed a Table for solid timber construction. However, the insulation R values proposed for the solid timber walls were high enough that the factories concerned would have encountered extreme difficulties in meeting the Table requirements and the calculations seemed to take into account only insulation values and disregarded thermal mass. SWBI needed to be able to prove that the thermal insulation properties of timber, plus the thermal mass properties of timber, would produce houses which complied with the revised H1 and would be able to be manufactured without undue complication and cost SWBI was also interested in proving the ability of wood to moderate internal moisture levels in houses. The calls for increased weathertightness, draft proofing and thermal insulation were raising the possibilities of high and prolonged moisture levels within houses, with detrimental effects on building fabric, furnishings and occupant health. At the same time, society was being warned and starting to appreciate the messages about global warming and climate change. In all this, the common element was carbon. Minimising carbon dioxide emissions, or even storing carbon dioxide in some way, became relevant.

3 And solid timber houses are a great way of storing CO 2 for long periods.(see the NZ Wood carbon calculator ( for the difference between carbon stored in a conventional timber framed house versus a solid wood house.) Literature searches found some remarkably relevant work done by researchers such as Hameury, and SWBI felt that we could make great headway in improving the acceptance of solid wood buildings in the modern world by using such techniques. SWBI decided to employ eminent and independent researchers to determine the facts and thus provide a basis for future compliance issues and for marketing efforts. Specific targets for research were 1. investigate the combined benefits of timbers thermal conductivity and thermal mass in reducing the energy required to heat and cool a home 2. investigate the ability of wooden walls to moderate internal moisture within a home 3. determine potential energy savings due to solid wood s superior thermal mass 4. investigate the effect of wood s ability to generate and absorb heat with changes in moisture content. Means of achieving these targets were discussed by SWBI a. build structures of non-solid and solid construction, with equivalent R values on environmentally identical sites, and monitor the temperatures within, and power inputs required to keep within defined indoor environment limits b. construct virtual buildings using acknowledged credible software and run simulations over seasons. a. build structures of non-solid and solid construction, with equivalent R values on environmentally identical sites, and monitor the humidities within, and power inputs required to keep within defined indoor environment limits b. construct virtual buildings using acknowledged credible software and run simulations of internal humidities over seasons. 3. run simulations to determine possible energy savings using solid wood buildings 4. a. conduct laboratory measurements of temperature changes with changes in moisture absorption in pieces of timber b. use software developed to predict heat flow into and out of timber walls with changes in humidity. In all 4 cases it was decided to use the software modelling approach, as a wide range of concepts and proprietary designs could be trialled, whereas in situ testing would have required greater expense and less opportunity to try variations.

4 It was decided to contract Dr Larry Bellamy and Dr Don McKenzieto carry out research into targets 1, 2 and 3, and to contract the Wood Drying Group of Ensis Ltd (SCION + CSIRO collaboration) to carry out part 4. Bellamy et al undertook 1. To determine R-values for solid wood construction with energy performance nearly equal to that of light timber frame construction insulated to the R- values proposed by the Department of Building and Housing, in its November 2006 consultation document. Results from this analysis, which ignores moisture exchange between the indoor air and the building fabric, will underpin a new set of proposed R-values for solid wood construction for use in the New Zealand Building Code. 2. To determine the effects of surface coatings and moisture exchange between the indoor air and the building fabric on the energy performance and indoor humidity of solid wood and light timber frame homes. Results from this part of the analysis are used to determine the energy and humidity advantages of solid wood construction compared with light timber frame and plasterboard construction. 3. To determine the potential energy savings when a New Zealand home is built with exterior-insulated solid wood external walls and solid wood internal walls instead of timber frame walls. Ensis undertook 4. To determine the effect of heat of wetting on wall surface temperature in solid timber walls. Method. Bellamy et al methods were The energy and humidity advantages of solid wood construction were determined using the BSim (version 4,6,8,22 with moisture extension) dynamic building energy program supplied by the Danish Building Research Institute [4]. BSim was used to simulate the energy flows and indoor environment in a model home over a typical meteorological year, at Auckland (37 o S) and Christchurch (43.5 o S). The timber frame construction R values (roof, wall, floor and joinery) used for comparison were a matrix of the (then) current and proposed values proposed by DBH. The proposed timber frame values were modified by DBH before publication and the equivalent solid timber values produced by the work reported here were also modified to maintain equivalency Ensis method was The one dimensional single-board drying model has been modified to take into account the heat of sorption (wetting or drying) component in the energy balance in addition to the heat of vaporisation. The model can select appropriate temperature and

5 RH depending on the time of the day, day of the month for a particular place from an input file or user can specify temperature and RH. The model then predicts the temperature and MC of the surface of wooden wall for this given condition over time. The model assumes the same conditions on both sides of the wall. It is in fact simulating the changes of the surface of internal unsealed bare wooden wall to changes in internal conditions. Results. 1. Bellamy found for comparative R values for light timber framed walls vs solid timber walls:- The results show that the energy performance with 40 mm thick solid wood internal walls is similar to that with timber frame internal walls. Timber frame internal walls are outperformed by 60 mm and 90 mm thick solid wood internal walls. A smaller external wall R-value is required when these solid wood walls are used in place of timber frame walls. The energy advantage of relatively thick solid wood internal walls is due to their greater thermal mass compared with timber frame construction. The results indicate that the energy advantage of solid wood internal walls is slightly greater than that of solid wood external walls with equal wood thickness. This may be explained by the fact that nearly all of the heat stored in internal walls is returned to the indoor space, while some heat stored in external walls is lost to the outdoors, so these walls are not as efficient at storing heat. Results also show that the use of 35 mm thick wood ceilings instead of plasterboard ceilings has a small effect, if any, on external wall R-value. And the same is true when 40 mm thick solid wood external walls are used in place of timber frame external walls. While there appears to be little energy advantage in using 40 mm thick solid wood rather than timber frame in external walls, there is a significant advantage in using 60 mm or 90 mm thick solid wood. Significantly smaller external wall R-values are required if solid wood is used in external walls, internal walls and ceilings. Take, for example, a construction comprising 90 mm thick solid wood external walls, 60 mm thick solid wood internal walls and 35 mm thick wood ceilings. In this case the external wall R-value for solid wood construction is R0.7 at Auckland compared with R1.3 for timber frame. The external wall R-value for solid wood construction is R1.3 at Christchurch compared with R1.9 for timber frame. 2. Main points of Bellamy s results for humidity performance of solid wood are :- Indoor humidity with uncoated solid wood construction is similar to, or slightly higher than, the humidity with timber frame construction during the daytime and is significantly lower during the night. The moisture buffering effect of solid wood can be expected to increase with decreasing flow of outside air through the building. There is less ventilation during the night, which helps to explain why solid wood has a greater effect on humidity during the night than during the day.

6 The monthly mean humidity in the master bedroom of the model house is up to 4% lower with solid wood construction compared with timber frame construction. A greater reduction is observed if the bedroom door is closed during the night, thus restricting air circulation with the rest of the house. Simulations indicate that the use of solid wood rather than timber frame construction reduces monthly mean humidity in the bedroom by more than 5% when the bedroom door is closed. Humidity is in the desirable range (30-60%): 14% and 40% of the time at Auckland for timber frame and solid wood construction respectively. 85% and 99% of the time at Christchurch for timber frame and solid wood construction respectively. These results show that excessive humidity is an important issue at Auckland, but less so at Christchurch. They also show that solid wood provides a significant humidity advantage by reducing the frequency of undesirably high indoor humidity. 3. It can be seen from Figures 1 and 2 below that heating, cooling and total energy use are reduced when a home is built with exterior-insulated solid wood external walls and solid wood internal walls, instead of timber frame walls. This statement is true for Auckland and Christchurch, indicating that the superior thermal mass of solid wood construction provides an energy advantage in warm and cool climates. The percentage savings in total energy use depends on the thickness of the solid wood walls, external wall R-value and the location. For 45 mm solid wood, the savings range from % at Auckland and % at Christchurch, with savings increasing with increasing R-value. For 60 mm solid wood, the savings range from % at Auckland and % at Christchurch. While the percentage savings in energy use are greatest at Auckland, the absolute savings are greatest at Christchurch. Figure 1 Annual heating, cooling and total energy use of the model house at Auckland for timber frame, 45 mm solid wood and 60 mm solid wood wall constructions. R3.1 roof, R0.26 windows and R1.3 floor. (See Table 1 for description of constructions.) Frame 45 Wood 60 Wood Energy Use (kwh/m 2 (floor)) 12 8 Total Heating 4 Cooling Wall Total R-value (m 2K/W)

7 Figure 2 Annual heating, cooling and total energy use of the model house at Christchurch for timber frame, 45 mm solid wood and 60 mm solid wood wall constructions. R3.5 roof, R0.26 windows and R1.9 floor Frame 45 Wood 60 Wood Energy Use (kwh/m 2 (floor)) Total Heating 4 Cooling Wall Total R-value (m 2K/W) This work eventually resulted in a relatively complex matrix of wall R values and wall thicknesses, which can be seen in Replacement Table 2 a of H1. These constructions, which generally require insulation external to the timber wall, are not necessarily those of any particular solid timber manufacturer, but may be used as a comparison value for proving compliance to H1 using the calculation or modelling methods of H1 / AS1. 4. Ensis results for heat of wetting are:- The largest effect of heat of wetting occurs around 2pm, when the difference between wall-air temperature gradients due to heat of wetting is greatest (0.3ºC). Looking at heat transferred by convection, Table 1 shows that there is a difference of 0.9 W/m 2 between the with and without heat of wetting cases. Mostly the difference is negligible. Thus we will assume a maximum of 1 W/m 2. In a room with 55 m 2 of exposed surface this is equivalent to 55W of heat transfer. This is less than energy that is released from an incandescent light bulb, and it is unlikely that this amount of heat or cooling would be noticeable.

8 Conclusions The analysis confirms that the energy performance of solid wood construction is superior to that of timber frame construction for equivalent wall R values. The superior energy performance is almost entirely due to solid wood s greater thermal mass, ie. its capacity to store and exchange heat. The type of construction used in internal walls has a significant effect on home energy performance. The results show that solid wood external wall R-values lower than proposed [by DBH] can be justified if a home is constructed with solid wood internal walls rather than timber frame internal walls. Solid wood walls and ceiling have a significant effect on ameliorating internal moisture, reducing higher humidity levels in bedrooms at night, and returning moisture to atmosphere during the day. The heat of wetting of wood has very little effect on internal temperature. While there can be a release of up to 1 Watt per square metre of timber surface, in essence this is not a significant amount of energy and would hardly be noticeable in a house. The overall result was that Department of Building and Housing agreed to insert suitable Tables for minimum R values for solid wood houses in Clause H1 Energy Efficiency of the NZ Building Code, and SWBI could proceed with marketing the benefits of solid wood homes with technical confidence. References. Haque N, Riley S, and Bayne K 2006 Solid Wood Building Initiative Heat of Wetting Model Ensis Client Report Hameury S 2006 The Hygrothermal Inertia of Massive Timber Constructions Doctoral Thesis Stockholm Bellamy L and Mackenzie D 2006 Energy and Comfort Performance of Solid Wood Buildings: Literature Review Bellamy L and Mackenzie D 2007 Simulation analysis of the energy performance and humidity of solid wood and light timber frame homes Solid Wood Stage 2 Final Report.