## 2 Materials and Methods  
Two full-scale wall sections were constructed at the Energy and Building Design laboratory (EBD-lab) at Lund University (see Figure 3). This is a facility where the energy performance of entire wall sections can be tested. There are two individual test rooms with fully insulated internal walls, floors and ceilings. The facade sections for these rooms can be lifted out and new facades put in. The test facades were south-facing. As there was only one external wall per test room, there was only one wall through which there was energy loss towards the outdoor climate. Energy use for heating the test rooms was monitored over a one-year period. Energy loss through the internal walls, floor, and roof was kept to a minimum by keeping the indoor temperature in the surrounding lab at ambient temperature. Figure 2: (**a**) Clay mortar with straw in an inner layer between wooden slats on a rendered timber house in Sweden. Photo: [PERSON]. (**b**) Old mortars from a rendered facade in Visby. It contains clay, a little lime and straw, and was used as mortar in the inner 5 cm layer between wooden slats, behind a lime render. Photo: [PERSON]. The indoor temperature inside the two test rooms was kept within the interval 19.0-22.0 \({}^{\circ}\)C. At low outdoor temperatures, as soon as the temperature dropped to 19 \({}^{\circ}\)C, the heating system would start. The room was heated by means of the ventilation system. When heating started, the ventilation system started, distributing warm air from the ventilation system evenly throughout the whole room. As soon as the indoor temperature reached 22 \({}^{\circ}\)C, the heating system would stop. When outdoor temperatures were lower than 19 \({}^{\circ}\)C, the temperature inside the room would drop, until it went below 19 \({}^{\circ}\)C, and then heating would start again. Hence, the temperature inside the rooms during the heating season was within the interval 19-22 \({}^{\circ}\)C. There was no active cooling, so in the summer, the indoor temperature would exceed 22 \({}^{\circ}\)C without any active cooling measures. The temperature inside the test rooms was measured every six minutes. Energy use for space heating was monitored continuously, with one measurement point every six minutes. Relative humidity in the rooms was measured using TESTO devices. Two devices were installed in each room--one mounted directly on the internal surface of the outer wall, the other near the entrance door. The TESTO devices measured relative humidity and temperature continuously, with one measurement per hour. The wall sections measured 2.7 \(\times\) 3.1 m (width \(\times\) height). Traditional post-and-plank walls were built in each external wall section (see Figures 4-9). One wall section (A) was built as a traditional post-and-plank wall with a lime render while the other wall section (B) was a post-and-plank wall with a hemp-lime render. These walls resembled a historic post-and-plank wall _before_ renovation and a historic post-and-plank wall _after_ renovation with hemp-lime. Both of the walls had a lime render as an external wall finish. The external walls were built up as follows, as seen from the inside:  
* (\"before renovation\"):
* Traditional paper covering
* Post-and-plank structure with 2\" planks (50 mm)
* Lime render (80 mm) with diagonal wooden slats (30 \(\times\) 36 mm), approx. c.o.c. 200 mm
* **Lime render** (20 mm)  
Hemp-lime-facade** (\"after renovation\"): * Traditional paper covering * Post-and-plank structure with 2\" planks (50 mm) * Hemp-lime render (90 mm) with diagonal wooden slats (30 \(\times\) 36 mm), approx. c.o.c. 200 mm
* Lime render (20 mm)  
Two different lime renders were applied to the walls. Each wall was divided in two equal sections, approximately 1.3 m wide. On one section, an air lime (Nordkalk SL) 1:1.5 was applied, and on the other a natural hydraulic lime (St. Astier NHL 3,5) 1:1.5. Hemp shiv were supplied by BFA Neu GmbH in Germany. The hemp-lime render was mixed in a horizontal cement mixer on site.